Common structs for Helm

This PR adds `pkg/inject/template-values.go` which contains the structs
needed to set the helm variables during injection. They can also be
leveraged during installation:

```
package inject

type (
        // Image contains the details to define a container image
        Image struct {
                Name       string
                PullPolicy string
                Version    string
        }

        // Port contains all the port-related setups
        Port struct {
                Admin               int32
                Control             int32
                Inbound             int32
                Outbound            int32
                IgnoreInboundPorts  string
                IgnoreOutboundPorts string
        }

        // Constraints wraps the Limit and Request settings for computational resources
        Constraints struct {
                Limit   string
                Request string
        }

        // Resources represents the computational resources setup for a given container
        Resources struct {
                CPU    Constraints
                Memory Constraints
        }

        // Identity contains the fields to set the identity variables in the proxy
        // sidecar container
        Identity struct {
                TrustDomain  string
                TrustAnchors string
        }

        // Proxy contains the fields to set the proxy sidecar container
        Proxy struct {
                Component             string
                ClusterDomain         string
                DisableIdentity       bool
                EnableExternalProfile bool
                HighAvailability      bool
                Identity              *Identity
                Image                 Image
                LogLevel              string
                ControlPlaneNamespace string
                Port                  Port
                UID                   int64
                ResourceRequirements  *Resources
        }

        // ProxyInit contains the fields to set the proxy-init container
        ProxyInit struct {
                Image                Image
                Port                 Port
                UID                  int64
                ResourceRequirements *Resources
        }
)
```

Signed-off-by: Alejandro Pedraza <alejandro@buoyant.io>

pkg/inject/template-values.go

@@ -0,0 +1,63 @@
+package inject
+
+type (
+	// Image contains the details to define a container image
+	Image struct {
+		Name       string
+		PullPolicy string
+		Version    string
+	}
+
+	// Port contains all the port-related setups
+	Port struct {
+		Admin               int32
+		Control             int32
+		Inbound             int32
+		Outbound            int32
+		IgnoreInboundPorts  string
+		IgnoreOutboundPorts string
+	}
+
+	// Constraints wraps the Limit and Request settings for computational resources
+	Constraints struct {
+		Limit   string
+		Request string
+	}
+
+	// Resources represents the computational resources setup for a given container
+	Resources struct {
+		CPU    Constraints
+		Memory Constraints
+	}
+
+	// Identity contains the fields to set the identity variables in the proxy
+	// sidecar container
+	Identity struct {
+		TrustDomain  string
+		TrustAnchors string
+	}
+
+	// Proxy contains the fields to set the proxy sidecar container
+	Proxy struct {
+		Component             string
+		ClusterDomain         string
+		DisableIdentity       bool
+		EnableExternalProfile bool
+		HighAvailability      bool
+		Identity              *Identity
+		Image                 Image
+		LogLevel              string
+		ControlPlaneNamespace string
+		Port                  Port
+		UID                   int64
+		ResourceRequirements  *Resources
+	}
+
+	// ProxyInit contains the fields to set the proxy-init container
+	ProxyInit struct {
+		Image                Image
+		Port                 Port
+		UID                  int64
+		ResourceRequirements *Resources
+	}
+)