### 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
import base64
import datetime
import json
import logging
import re
import time
from typing import Any, Dict, Optional, Tuple, Union
from urllib.parse import urljoin
import pytz
import requests
from flask import Response as FlaskResponse
from jsonschema import ValidationError, validate
from requests.models import Response
from localstack import config
from localstack.constants import (
    APPLICATION_JSON,
    HEADER_LOCALSTACK_EDGE_URL,
    LOCALHOST_HOSTNAME,
    PATH_USER_REQUEST,
    TEST_AWS_ACCOUNT_ID,
)
from localstack.services.apigateway import helpers