feat(ec2): add support for environment files and variables in systemd (…

…#29629)

### Reason for this change


Allow users to define `Environment` and `EnvironmentFile` in a systemd service file.

### Description of changes


Added 2 new properties for `ec2.InitService.systemdConfigFile`:
1. `environmentVariables` which is a string key value pair
2. `environmentFiles` which is a list of file paths

### Description of how you validated changes


I have added a unit test.
Documentations referred to:
- https://www.freedesktop.org/software/systemd/man/latest/systemd.exec.html#EnvironmentFile=
- https://www.freedesktop.org/software/systemd/man/latest/systemd.exec.html#Environment= 

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk-testing/framework-integ/test/aws-ec2/test/integ.instance-init.js.snapshot/integ-init.template.json

@@ -18,9 +18,6 @@
   "IntegInitVpcPublicSubnet1Subnet41A6F6D4": {
    "Type": "AWS::EC2::Subnet",
    "Properties": {
-    "VpcId": {
-     "Ref": "IntegInitVpc0D4FCCB3"
-    },
     "AvailabilityZone": {
      "Fn::Select": [
       0,
@@ -44,21 +41,24 @@
       "Key": "Name",
       "Value": "integ-init/IntegInitVpc/PublicSubnet1"
      }
-    ]
+    ],
+    "VpcId": {
+     "Ref": "IntegInitVpc0D4FCCB3"
+    }
    }
   },
   "IntegInitVpcPublicSubnet1RouteTable837CD5FB": {
    "Type": "AWS::EC2::RouteTable",
    "Properties": {
-    "VpcId": {
-     "Ref": "IntegInitVpc0D4FCCB3"
-    },
     "Tags": [
      {
       "Key": "Name",
       "Value": "integ-init/IntegInitVpc/PublicSubnet1"
      }
-    ]
+    ],
+    "VpcId": {
+     "Ref": "IntegInitVpc0D4FCCB3"
+    }
    }
   },
   "IntegInitVpcPublicSubnet1RouteTableAssociation00D33741": {
@@ -75,12 +75,12 @@
   "IntegInitVpcPublicSubnet1DefaultRoute5BB90E8C": {
    "Type": "AWS::EC2::Route",
    "Properties": {
-    "RouteTableId": {
-     "Ref": "IntegInitVpcPublicSubnet1RouteTable837CD5FB"
-    },
     "DestinationCidrBlock": "0.0.0.0/0",
     "GatewayId": {
      "Ref": "IntegInitVpcIGWF019AC85"
+    },
+    "RouteTableId": {
+     "Ref": "IntegInitVpcPublicSubnet1RouteTable837CD5FB"
     }
    },
    "DependsOn": [
@@ -102,15 +102,15 @@
   "IntegInitVpcPublicSubnet1NATGateway46F32F7F": {
    "Type": "AWS::EC2::NatGateway",
    "Properties": {
-    "SubnetId": {
-     "Ref": "IntegInitVpcPublicSubnet1Subnet41A6F6D4"
-    },
     "AllocationId": {
      "Fn::GetAtt": [
       "IntegInitVpcPublicSubnet1EIP46FCC3D6",
       "AllocationId"
      ]
     },
+    "SubnetId": {
+     "Ref": "IntegInitVpcPublicSubnet1Subnet41A6F6D4"
+    },
     "Tags": [
      {
       "Key": "Name",
@@ -126,9 +126,6 @@
   "IntegInitVpcPublicSubnet2Subnet9A384F16": {
    "Type": "AWS::EC2::Subnet",
    "Properties": {
-    "VpcId": {
-     "Ref": "IntegInitVpc0D4FCCB3"
-    },
     "AvailabilityZone": {
      "Fn::Select": [
       1,
@@ -152,21 +149,24 @@
       "Key": "Name",
       "Value": "integ-init/IntegInitVpc/PublicSubnet2"
      }
-    ]
+    ],
+    "VpcId": {
+     "Ref": "IntegInitVpc0D4FCCB3"
+    }
    }
   },
   "IntegInitVpcPublicSubnet2RouteTableF7E8F920": {
    "Type": "AWS::EC2::RouteTable",
    "Properties": {
-    "VpcId": {
-     "Ref": "IntegInitVpc0D4FCCB3"
-    },
     "Tags": [
      {
       "Key": "Name",
       "Value": "integ-init/IntegInitVpc/PublicSubnet2"
      }
-    ]
+    ],
+    "VpcId": {
+     "Ref": "IntegInitVpc0D4FCCB3"
+    }
    }
   },
   "IntegInitVpcPublicSubnet2RouteTableAssociationB816F9F3": {
@@ -183,12 +183,12 @@
   "IntegInitVpcPublicSubnet2DefaultRoute2393995F": {
    "Type": "AWS::EC2::Route",
    "Properties": {
-    "RouteTableId": {
-     "Ref": "IntegInitVpcPublicSubnet2RouteTableF7E8F920"
-    },
     "DestinationCidrBlock": "0.0.0.0/0",
     "GatewayId": {
      "Ref": "IntegInitVpcIGWF019AC85"
+    },
+    "RouteTableId": {
+     "Ref": "IntegInitVpcPublicSubnet2RouteTableF7E8F920"
     }
    },
    "DependsOn": [
@@ -210,15 +210,15 @@
   "IntegInitVpcPublicSubnet2NATGateway9CCB4A9C": {
    "Type": "AWS::EC2::NatGateway",
    "Properties": {
-    "SubnetId": {
-     "Ref": "IntegInitVpcPublicSubnet2Subnet9A384F16"
-    },
     "AllocationId": {
      "Fn::GetAtt": [
       "IntegInitVpcPublicSubnet2EIP553B40DC",
       "AllocationId"
      ]
     },
+    "SubnetId": {
+     "Ref": "IntegInitVpcPublicSubnet2Subnet9A384F16"
+    },
     "Tags": [
      {
       "Key": "Name",
@@ -234,9 +234,6 @@
   "IntegInitVpcPrivateSubnet1Subnet259B51C1": {
    "Type": "AWS::EC2::Subnet",
    "Properties": {
-    "VpcId": {
-     "Ref": "IntegInitVpc0D4FCCB3"
-    },
     "AvailabilityZone": {
      "Fn::Select": [
       0,
@@ -260,21 +257,24 @@
       "Key": "Name",
       "Value": "integ-init/IntegInitVpc/PrivateSubnet1"
      }
-    ]
+    ],
+    "VpcId": {
+     "Ref": "IntegInitVpc0D4FCCB3"
+    }
    }
   },
   "IntegInitVpcPrivateSubnet1RouteTableCB37994B": {
    "Type": "AWS::EC2::RouteTable",
    "Properties": {
-    "VpcId": {
-     "Ref": "IntegInitVpc0D4FCCB3"
-    },
     "Tags": [
      {
       "Key": "Name",
       "Value": "integ-init/IntegInitVpc/PrivateSubnet1"
      }
-    ]
+    ],
+    "VpcId": {
+     "Ref": "IntegInitVpc0D4FCCB3"
+    }
    }
   },
   "IntegInitVpcPrivateSubnet1RouteTableAssociation067DEF9D": {
@@ -291,21 +291,18 @@
   "IntegInitVpcPrivateSubnet1DefaultRoute654ACECF": {
    "Type": "AWS::EC2::Route",
    "Properties": {
-    "RouteTableId": {
-     "Ref": "IntegInitVpcPrivateSubnet1RouteTableCB37994B"
-    },
     "DestinationCidrBlock": "0.0.0.0/0",
     "NatGatewayId": {
      "Ref": "IntegInitVpcPublicSubnet1NATGateway46F32F7F"
+    },
+    "RouteTableId": {
+     "Ref": "IntegInitVpcPrivateSubnet1RouteTableCB37994B"
     }
    }
   },
   "IntegInitVpcPrivateSubnet2Subnet1643B059": {
    "Type": "AWS::EC2::Subnet",
    "Properties": {
-    "VpcId": {
-     "Ref": "IntegInitVpc0D4FCCB3"
-    },
     "AvailabilityZone": {
      "Fn::Select": [
       1,
@@ -329,21 +326,24 @@
       "Key": "Name",
       "Value": "integ-init/IntegInitVpc/PrivateSubnet2"
      }
-    ]
+    ],
+    "VpcId": {
+     "Ref": "IntegInitVpc0D4FCCB3"
+    }
    }
   },
   "IntegInitVpcPrivateSubnet2RouteTable030EC93B": {
    "Type": "AWS::EC2::RouteTable",
    "Properties": {
-    "VpcId": {
-     "Ref": "IntegInitVpc0D4FCCB3"
-    },
     "Tags": [
      {
       "Key": "Name",
       "Value": "integ-init/IntegInitVpc/PrivateSubnet2"
      }
-    ]
+    ],
+    "VpcId": {
+     "Ref": "IntegInitVpc0D4FCCB3"
+    }
    }
   },
   "IntegInitVpcPrivateSubnet2RouteTableAssociation6B52BD72": {
@@ -360,12 +360,12 @@
   "IntegInitVpcPrivateSubnet2DefaultRoute6A10B6EA": {
    "Type": "AWS::EC2::Route",
    "Properties": {
-    "RouteTableId": {
-     "Ref": "IntegInitVpcPrivateSubnet2RouteTable030EC93B"
-    },
     "DestinationCidrBlock": "0.0.0.0/0",
     "NatGatewayId": {
      "Ref": "IntegInitVpcPublicSubnet2NATGateway9CCB4A9C"
+    },
+    "RouteTableId": {
+     "Ref": "IntegInitVpcPrivateSubnet2RouteTable030EC93B"
     }
    }
   },
@@ -383,11 +383,11 @@
   "IntegInitVpcVPCGW85EDC292": {
    "Type": "AWS::EC2::VPCGatewayAttachment",
    "Properties": {
-    "VpcId": {
-     "Ref": "IntegInitVpc0D4FCCB3"
-    },
     "InternetGatewayId": {
      "Ref": "IntegInitVpcIGWF019AC85"
+    },
+    "VpcId": {
+     "Ref": "IntegInitVpc0D4FCCB3"
     }
    }
   },
@@ -513,7 +513,7 @@
     ]
    }
   },
-  "Instance255F35265a0c5f577d761edb0": {
+  "Instance255F3526574cbd507dfce8b71": {
    "Type": "AWS::EC2::Instance",
    "Properties": {
     "AvailabilityZone": {
@@ -553,23 +553,23 @@
       "Fn::Join": [
        "",
        [
-        "#!/bin/bash\n# fingerprint: 89cb2e09a1c3d4c8\n(\n  set +e\n  /opt/aws/bin/cfn-init -v --region ",
+        "#!/bin/bash\n# fingerprint: 4f2827c68bde31b4\n(\n  set +e\n  /opt/aws/bin/cfn-init -v --region ",
         {
          "Ref": "AWS::Region"
         },
         " --stack ",
         {
          "Ref": "AWS::StackName"
         },
-        " --resource Instance255F35265a0c5f577d761edb0 -c default\n  /opt/aws/bin/cfn-signal -e $? --region ",
+        " --resource Instance255F3526574cbd507dfce8b71 -c default\n  /opt/aws/bin/cfn-signal -e $? --region ",
         {
          "Ref": "AWS::Region"
         },
         " --stack ",
         {
          "Ref": "AWS::StackName"
         },
-        " --resource Instance255F35265a0c5f577d761edb0\n  cat /var/log/cfn-init.log >&2\n)"
+        " --resource Instance255F3526574cbd507dfce8b71\n  cat /var/log/cfn-init.log >&2\n)"
        ]
       ]
      }
@@ -641,6 +641,24 @@
         "group": "root"
        }
       }
+     },
+     "service": {
+      "files": {
+       "/myvars.env": {
+        "content": "OTHER_VAR=\"im from the file :3\"",
+        "encoding": "plain",
+        "mode": "000644",
+        "owner": "root",
+        "group": "root"
+       },
+       "/etc/systemd/system/myapp.service": {
+        "content": "[Unit]\nAfter=network.target\n[Service]\nExecStart=/bin/bash -c \"echo HELLO_WORLD=${MY_VAR} | FROM_FILE=${OTHER_VAR}\"\nRestart=always\nEnvironmentFile=/myvars.env\nEnvironment=\"MY_VAR=its me :)\"\n[Install]\nWantedBy=multi-user.target",
+        "encoding": "plain",
+        "mode": "000644",
+        "owner": "root",
+        "group": "root"
+       }
+      }
      }
     },
     "AWS::CloudFormation::Authentication": {