Missing CONTRIBUTION.md or CODE_OF_CONDUCT.md

![image](https://github.com/novuhq/novu-rust/assets/54350721/b588bc23-1a2f-418a-8118-9fc55e06a750)
Based on official [Open Source Guide](https://opensource.guide/how-to-contribute/) and mode of contributions made so far to the novuhq repo, happy to draft a `CONTRIBUTION.md or CODE_OF_CONDUCT.md` for novu-rust to help guide contributors, especially first-time open source contributors.