### 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
cert_pem_file = get_cert_pem_file_path()
        return generate_ssl_cert(cert_pem_file, serial_number=serial_number)
    @classmethod
    def get_flask_ssl_context(cls, serial_number=None):
        if config.USE_SSL:
            _, cert_file_name, key_file_name = cls.create_ssl_cert(serial_number=serial_number)
            return cert_file_name, key_file_name
        return None
class UrlMatchingForwarder(ProxyListener):
    """
    ProxyListener that matches URLs to a base url pattern, and if the request url matches the
    pattern, forwards it to
    a forward_url. See TestUrlMatchingForwarder for how it behaves.
    """
    def __init__(self, base_url: str, forward_url: str) -> None:
        super().__init__()
        self.base_url = urlparse(base_url)
        self.forward_url = urlparse(forward_url)
    def forward_request(self, method, path, data, headers):
        host = headers.get("Host", "")
        if not self.matches(host, path):
            return True
        
        forward_url = self.build_forward_url(host, path)
        
        headers["Host"] = forward_url.netloc
        
        return self.do_forward(method, forward_url.geturl(), headers, data)
    def do_forward(self, method, url, headers, data):