### 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_url = target_url or "%s://%s:%s" % (config.get_protocol(), LOCALHOST, port)
    url = "%s%s" % (target_url, path)
    response = requests.request(
        method, url, data=data, headers=headers, verify=False, stream=True, allow_redirects=False
    )
    return response
def get_auth_string(method, path, headers, data=None):
    """
    Get Auth header from Header (this is how aws client's like boto typically