### 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
if cors:
        CORS(app)
    if not config.DEBUG:
        logging.getLogger("werkzeug").setLevel(logging.ERROR)
    if not host:
        host = "0.0.0.0"
    ssl_context = None
    if not config.FORWARD_EDGE_INMEM:
        ssl_context = GenericProxy.get_flask_ssl_context(serial_number=port)
    app.config["ENV"] = "development"
    def noecho(*args, **kwargs):
        pass
    try:
        import click
        click.echo = noecho
    except Exception:
        pass
    def _run(*_):
        app.run(port=int(port), threaded=True, host=host, ssl_context=ssl_context)
        return app
    if asynchronous:
        return start_thread(_run)
    return _run()