### 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
match = re.match(PATH_REGEX_TEST_INVOKE_API, path)
            invocation_context.method = match[3]
            if data:
                orig_data = data
                path_with_query_string = orig_data.get("pathWithQueryString", None)
                if path_with_query_string:
                    invocation_context.path_with_query_string = path_with_query_string
                invocation_context.data = data.get("body")
                invocation_context.headers = orig_data.get("headers", {})
            result = invoke_rest_api_from_request(invocation_context)
            result = {
                "status": result.status_code,
                "body": to_str(result.content),
                "headers": dict(result.headers),
            }
            return result
        return True
    def return_response(self, method, path, data, headers, response):
        
        if re.match(r"/restapis/[^/]+/documentation/versions", path):
            if response.status_code == 404:
                return requests_response({"position": "1", "items": []})
        
        if response.status_code == 404:
            result = None
            if path == "/account":
                data = data and json.loads(to_str(data))
                result = handle_accounts(method, path, data, headers)
            elif path.startswith("/vpclinks"):
                data = data and json.loads(to_str(data))