### 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
template = "#set ($bar = $input.path('$.foo')[1]) \n $bar"
        context = {"foo": ["e1", "e2", "e3", "e4"]}
        result = render_velocity_template(template, context).strip()
        assert result == "e2"
        template = "#set ($bar = $input.path('$.foo')[1][1][1]) $bar"
        context = {"foo": [["e1"], ["e2", ["e3", "e4"]]]}
        result = render_velocity_template(template, context).strip()
        assert result == "e4"
    def test_string_methods(self):
        context = {"foo": {"bar": "BAZ baz"}}
        template1 = "${foo.bar.strip().lower().replace(' ','-')}"
        template2 = "${foo.bar.trim().toLowerCase().replace(' ','-')}"
        for template in [template1, template2]:
            result = render_velocity_template(template, {}, variables=context)
            assert result == "baz-baz"
    def test_render_urlencoded_string_data(self):
        template = "MessageBody=$util.base64Encode($input.json('$'))"
        result = render_velocity_template(template, b'{"spam": "eggs"}')
        assert result == "MessageBody=eyJzcGFtIjogImVnZ3MifQ=="
    def test_construct_json_using_define(self):
        template = APIGW_TEMPLATE_CONSTRUCT_JSON
        context = {"p1": {"test": 123}, "p2": {"foo": "bar", "foo2": False}}
        result = render_velocity_template(template, context).strip()
        result = json.loads(result)
        assert result == {"p0": True, **context}