### 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
import re
from typing import Any, Callable, Dict, List, Optional, Set, Type, Union
from .collections import ensure_list
from .strings import first_char_to_lower
ComplexType = Union[List, Dict, object]
class ArbitraryAccessObj:
    """Dummy object that can be arbitrarily accessed - any attributes, as a callable, item assignment, ..."""
    def __init__(self, name=None):
        self.name = name
    def __getattr__(self, name, *args, **kwargs):
        return ArbitraryAccessObj(name)
    def __call__(self, *args, **kwargs):
        if self.name in ["items", "keys", "values"] and not args and not kwargs:
            return []
        return ArbitraryAccessObj()
    def __getitem__(self, *args, **kwargs):
        return ArbitraryAccessObj()
    def __setitem__(self, *args, **kwargs):
        return ArbitraryAccessObj()
class Mock(object):
    """Dummy class that can be used for mocking custom attributes."""
    pass
class ObjectIdHashComparator: