Add david as core developer and steering commitee CONTRIBUTING.md

[isabelle-dr]

Summary:

Update the contribution guidelines to have David as a core contributor and part of the steering commitee

Expected behavior:

Please make sure these boxes are checked before submitting your pull request - thanks!

• [ ] Run the unit tests with gradle test to make sure you didn't break anything
• Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• [ ] Linked all relevant issues
• [ ] Include screenshot(s) showing how this pull request works and fixes the issue(s)