### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

Currently the VTL template for `request_templates` is not processed properly:

```
#set( $body = $input.json("$") )

#macro( loop $map )
{
    #foreach($key in $map.keySet())
        #set( $k = $util.escapeJavaScript($key) )
        #set( $v = $util.escapeJavaScript($map.get($key)).replaceAll("\\'", "'") )
        "$k": "$v"
        #if( $foreach.hasNext ) , #end
    #end
}
#end

{
    "enhancedAuthContext": #loop($context.authorizer),

    "headers": #loop($input.params().header),

    "query": #loop($input.params().querystring),

    "path": #loop($input.params().path),

    "identity": #loop($context.identity),

    "stageVariables": #loop($stageVariables),
}
EOF
}
```

results in,

```
'

{
    "enhancedAuthContext": {
    }
,

    "headers": {
    }
,

    "query": {
    }
,

    "path": {
    }
,

    "identity": {
    }
,

    "stageVariables": {
    }
,
}
'
```

### Expected Behavior

The template should be rendered and have the JSON properties.

### How are you starting LocalStack?

Custom (please describe below)

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    awslocal s3 mb s3://mybucket


### Environment

```markdown
- OS: MacOS
- LocalStack: 0.14
```


### Anything else?

This example can be used to validate.
https://github.com/localstack/localstack-terraform-samples/tree/master/apigateway-lambda-velocity
__slots__ = ["invocation_context"]
    def __init__(self, invocation_context: ApiInvocationContext):
        self.invocation_context = invocation_context
    def invoke(self):
        try:
            data = self.invocation_context.data
            data = json.dumps(data) if isinstance(data, (dict, list)) else to_str(data)
            payload = apply_template(
                self.invocation_context.integration,
                "request",
                data,
                path_params=self.invocation_context.path_params,
                query_params=self.invocation_context.query_params(),
                headers=self.invocation_context.headers,
            )
        except Exception as e:
            LOG.warning("Failed to apply template for SNS integration", e)
            raise
        uri = (
            self.invocation_context.integration.get("uri")
            or self.invocation_context.integration.get("integrationUri")
            or ""
        )
        region_name = uri.split(":")[3]
        headers = aws_stack.mock_aws_request_headers(service="sns", region_name=region_name)
        return make_http_request(
            config.service_url("sns"), method="POST", headers=headers, data=payload
        )