### 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
target = headers.get("x-amz-target", "")
        auth_header = get_auth_string(method, path, headers, data)
        if auth_header and not headers.get("authorization"):
            headers["authorization"] = auth_header
        host = headers.get("host", "")
        orig_req_url = headers.pop(HEADER_LOCALSTACK_REQUEST_URL, "")
        headers[HEADER_LOCALSTACK_EDGE_URL] = (
            re.sub(r"^([^:]+://[^/]+).*", r"\1", orig_req_url) or "http://%s" % host
        )
        
        api, port, path, host = get_api_from_headers(headers, method=method, path=path, data=data)
        set_default_region_in_headers(headers)
        if port and int(port) < 0:
            return 404
        if not port:
            api, port = get_api_from_custom_rules(method, path, data, headers) or (
                api,
                port,
            )
        should_log_trace = is_trace_logging_enabled(headers)
        if api and should_log_trace:
            
            LOG.debug(
                'IN(%s): "%s %s" - headers: %s - data: %s', api, method, path, dict(headers), data
            )
        if not port:
            if method == "OPTIONS":
                if api and should_log_trace:
                    
                    LOG.debug('IN(%s): "%s %s" - status: %s', api, method, path, 200)