Add header generator and integrate it into HTTPX client

- Implement a fingerprint generator for generating real-world HTTP headers.
- Integrate it into [HttpxHttpClient](https://github.com/apify/crawlee-python/blob/master/src/crawlee/http_clients/httpx.py).
- [fingerprint-generator](https://github.com/apify/fingerprint-suite/tree/master/packages/fingerprint-generator) in TS could serve as an inspiration.