### 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
from __future__ import annotations
import functools
import json
import logging
import os
import re
import socket
import ssl
import threading
from asyncio.selector_events import BaseSelectorEventLoop
from typing import Dict, List, Match, Optional, Type, TypeVar, Union
from urllib.parse import parse_qs, unquote, urlencode, urlparse
import requests
from flask_cors import CORS
from flask_cors.core import (
    ACL_ALLOW_HEADERS,