feat(route53-targets): add AppSync route53 target (#31976)

### Issue # (if applicable)

Closes #26109

### Reason for this change

This PR adds support for creating alias records on AppSync's
`GraphqlApi`.

### Description of changes

- Add `appsync-target.ts` file, with the `AppSync` class.
- Add unit tests for this new `AppSync` target class.
- Update README.md of `aws-cdk-lib/aws-route53-targets`

### Description of how you validated changes

- Add unit tests

### 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*

---------

Co-authored-by: GZ <yuanhaoz@amazon.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

packages/@aws-cdk-testing/framework-integ/test/aws-route53-targets/test/integ.appsync-target.js.snapshot/aws-cdk-appsync-alias-integ.template.json

@@ -0,0 +1,142 @@
+{
+ "Resources": {
+  "apiC8550315": {
+   "Type": "AWS::AppSync::GraphQLApi",
+   "Properties": {
+    "AuthenticationType": "API_KEY",
+    "Name": "api"
+   }
+  },
+  "apiSchema0EA92056": {
+   "Type": "AWS::AppSync::GraphQLSchema",
+   "Properties": {
+    "ApiId": {
+     "Fn::GetAtt": [
+      "apiC8550315",
+      "ApiId"
+     ]
+    },
+    "Definition": "type test {\n  version: String!\n}\ntype Query {\n  getTests: [test]!\n}\ntype Mutation {\n  addTest(version: String!): test\n}\n"
+   }
+  },
+  "apiDomainNameBBFE36A4": {
+   "Type": "AWS::AppSync::DomainName",
+   "Properties": {
+    "CertificateArn": "arn:aws:acm:test-region:12345678:certificate/86468209-a272-595d-b831-0efb6421265z",
+    "Description": {
+     "Fn::Join": [
+      "",
+      [
+       "domain for api at ",
+       {
+        "Fn::GetAtt": [
+         "apiC8550315",
+         "GraphQLUrl"
+        ]
+       }
+      ]
+     ]
+    },
+    "DomainName": "*.example.com"
+   }
+  },
+  "apiDomainAssociation1CF2F52A": {
+   "Type": "AWS::AppSync::DomainNameApiAssociation",
+   "Properties": {
+    "ApiId": {
+     "Fn::GetAtt": [
+      "apiC8550315",
+      "ApiId"
+     ]
+    },
+    "DomainName": "*.example.com"
+   },
+   "DependsOn": [
+    "apiDomainNameBBFE36A4"
+   ]
+  },
+  "apiDefaultApiKey6AB8D7C4": {
+   "Type": "AWS::AppSync::ApiKey",
+   "Properties": {
+    "ApiId": {
+     "Fn::GetAtt": [
+      "apiC8550315",
+      "ApiId"
+     ]
+    }
+   },
+   "DependsOn": [
+    "apiSchema0EA92056"
+   ]
+  },
+  "Alias325C5727": {
+   "Type": "AWS::Route53::RecordSet",
+   "Properties": {
+    "AliasTarget": {
+     "DNSName": {
+      "Fn::GetAtt": [
+       "apiDomainNameBBFE36A4",
+       "AppSyncDomainName"
+      ]
+     },
+     "HostedZoneId": {
+      "Fn::FindInMap": [
+       "AWSCloudFrontPartitionHostedZoneIdMap",
+       {
+        "Ref": "AWS::Partition"
+       },
+       "zoneId"
+      ]
+     }
+    },
+    "HostedZoneId": "Z23ABC4XYZL05B",
+    "Name": "*.example.com.",
+    "Type": "A"
+   }
+  }
+ },
+ "Mappings": {
+  "AWSCloudFrontPartitionHostedZoneIdMap": {
+   "aws": {
+    "zoneId": "Z2FDTNDATAQYW2"
+   },
+   "aws-cn": {
+    "zoneId": "Z3RFFRIM2A3IF5"
+   }
+  }
+ },
+ "Parameters": {
+  "BootstrapVersion": {
+   "Type": "AWS::SSM::Parameter::Value<String>",
+   "Default": "/cdk-bootstrap/hnb659fds/version",
+   "Description": "Version of the CDK Bootstrap resources in this environment, automatically retrieved from SSM Parameter Store. [cdk:skip]"
+  }
+ },
+ "Rules": {
+  "CheckBootstrapVersion": {
+   "Assertions": [
+    {
+     "Assert": {
+      "Fn::Not": [
+       {
+        "Fn::Contains": [
+         [
+          "1",
+          "2",
+          "3",
+          "4",
+          "5"
+         ],
+         {
+          "Ref": "BootstrapVersion"
+         }
+        ]
+       }
+      ]
+     },
+     "AssertDescription": "CDK bootstrap stack version 6 required. Please run 'cdk bootstrap' with a recent version of the CDK CLI."
+    }
+   ]
+  }
+ }
+}