### 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 account_id:
        return account_id
    env = get_environment(env)
    if is_local_env(env):
        return os.environ["TEST_AWS_ACCOUNT_ID"]
    raise Exception("Unable to determine AWS account ID (%s, %s)" % (account_id, env))
def role_arn(role_name, account_id=None, env=None):
    if not role_name:
        return role_name
    if role_name.startswith("arn:aws:iam::"):
        return role_name
    env = get_environment(env)
    account_id = get_account_id(account_id, env=env)
    return "arn:aws:iam::%s:role/%s" % (account_id, role_name)
def policy_arn(policy_name, account_id=None):
    if ":policy/" in policy_name:
        return policy_name
    account_id = account_id or TEST_AWS_ACCOUNT_ID
    return "arn:aws:iam::{}:policy/{}".format(account_id, policy_name)
def iam_resource_arn(resource, role=None, env=None):
    env = get_environment(env)
    if not role:
        role = get_iam_role(resource, env=env)
    return role_arn(role_name=role, account_id=get_account_id())
def get_iam_role(resource, env=None):
    env = get_environment(env)
    return "role-%s" % resource
def secretsmanager_secret_arn(secret_id, account_id=None, region_name=None):