### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

We are using the `Authorization` header for routing purposes

```
 "authorization: AWS4-HMAC-SHA256 <...>"
```

https://github.com/localstack/localstack/issues/5770

### Expected Behavior

Use a custom header to avoid causing confusion with backend integrations

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

Run a custom HTTP integration without authorisation

### Environment

```markdown
- OS: 
- LocalStack:
```


### Anything else?

No
result = handle_vpc_links(method, path, data, headers)
            elif re.match(PATH_REGEX_CLIENT_CERTS, path):
                data = data and json.loads(to_str(data))
                result = handle_client_certificates(method, path, data, headers)
            if result is not None:
                response.status_code = 200
                aws_responses.set_response_content(response, result, getattr(result, "headers", {}))
        
        if method == "POST" and path == "/restapis":
            content = json.loads(to_str(response.content))
            api_id = content["id"]
            region = aws_stack.extract_region_from_auth_header(headers)
            API_REGIONS[api_id] = region
        
        if method == "POST" and path == "/restapis":
            content = json.loads(to_str(response.content))
            event_publisher.fire_event(
                event_publisher.EVENT_APIGW_CREATE_API,
                payload={"a": event_publisher.get_hash(content["id"])},
            )
        api_regex = r"^/restapis/([a-zA-Z0-9\-]+)$"
        if method == "DELETE" and re.match(api_regex, path):
            api_id = re.sub(api_regex, r"\1", path)
            event_publisher.fire_event(
                event_publisher.EVENT_APIGW_DELETE_API,
                payload={"a": event_publisher.get_hash(api_id)},
            )
class RequestValidator:
    __slots__ = ["context", "apigateway_client"]
    def __init__(self, context: ApiInvocationContext, apigateway_client):