### 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
pattern = "arn:aws:cognito-idp:%s:%s:userpool/%s"
    return _resource_arn(user_pool_id, pattern, account_id=account_id, region_name=region_name)
def kinesis_stream_arn(stream_name, account_id=None, region_name=None):
    pattern = "arn:aws:kinesis:%s:%s:stream/%s"
    return _resource_arn(stream_name, pattern, account_id=account_id, region_name=region_name)
def elasticsearch_domain_arn(domain_name, account_id=None, region_name=None):
    pattern = "arn:aws:es:%s:%s:domain/%s"
    return _resource_arn(domain_name, pattern, account_id=account_id, region_name=region_name)
def firehose_stream_arn(stream_name, account_id=None, region_name=None):
    pattern = "arn:aws:firehose:%s:%s:deliverystream/%s"
    return _resource_arn(stream_name, pattern, account_id=account_id, region_name=region_name)
def es_domain_arn(domain_name, account_id=None, region_name=None):
    pattern = "arn:aws:es:%s:%s:domain/%s"
    return _resource_arn(domain_name, pattern, account_id=account_id, region_name=region_name)
def kms_key_arn(key_id: str, account_id: str = None, region_name: str = None) -> str:
    pattern = "arn:aws:kms:%s:%s:key/%s"
    return _resource_arn(key_id, pattern, account_id=account_id, region_name=region_name)
def code_signing_arn(code_signing_id: str, account_id: str = None, region_name: str = None) -> str:
    pattern = "arn:aws:lambda:%s:%s:code-signing-config:%s"
    return _resource_arn(code_signing_id, pattern, account_id=account_id, region_name=region_name)
def ssm_parameter_arn(param_name: str, account_id: str = None, region_name: str = None) -> str: