### 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
if ":" in (secret_id or ""):
        return secret_id
    pattern = "arn:aws:secretsmanager:%s:%s:secret:%s"
    return _resource_arn(secret_id, pattern, account_id=account_id, region_name=region_name)
def cloudformation_stack_arn(stack_name, stack_id=None, account_id=None, region_name=None):
    stack_id = stack_id or "id-123"
    pattern = "arn:aws:cloudformation:%s:%s:stack/%s/{stack_id}".format(stack_id=stack_id)
    return _resource_arn(stack_name, pattern, account_id=account_id, region_name=region_name)
def cf_change_set_arn(change_set_name, change_set_id=None, account_id=None, region_name=None):
    change_set_id = change_set_id or "id-456"
    pattern = "arn:aws:cloudformation:%s:%s:changeSet/%s/{cs_id}".format(cs_id=change_set_id)
    return _resource_arn(change_set_name, pattern, account_id=account_id, region_name=region_name)
def dynamodb_table_arn(table_name, account_id=None, region_name=None):
    table_name = table_name.split(":table/")[-1]
    pattern = "arn:aws:dynamodb:%s:%s:table/%s"
    return _resource_arn(table_name, pattern, account_id=account_id, region_name=region_name)
def dynamodb_stream_arn(table_name, latest_stream_label, account_id=None):
    account_id = get_account_id(account_id)
    return "arn:aws:dynamodb:%s:%s:table/%s/stream/%s" % (
        get_region(),
        account_id,
        table_name,
        latest_stream_label,
    )
def cloudwatch_alarm_arn(alarm_name, account_id=None, region_name=None):
    pattern = "arn:aws:cloudwatch:%s:%s:alarm:%s"
    return _resource_arn(alarm_name, pattern, account_id=account_id, region_name=region_name)
def log_group_arn(group_name, account_id=None, region_name=None):