chore: create Flow Registry contribution guidelines

What does this merge request do and why?

It adds contribution and code review guidelines for Flow Registry framework setting up standards and procedures for development of the framework

closes #1381

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.
• If this change requires executor implementation: verified that issues/MRs exist for both Go executor and Node executor or confirmed that changes are backward-compatible and don't break existing executor functionality.