Docs: documentation updates

[isabelle-dr]

Summary:

• added acceptance test schema in ACCEPTANCE_TESTS.md
• remove Maxime from the steering committee
• add Kevin, Alexei and Artur to the list of core contributors
• add a mention of the monthly contributor meetings

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)

[emmambd]

@isabelle-dr This looks good to me! Only nit: is that the acceptance test workflow image still has a typo: dissapearing should be disappearing

[emmambd]

Only concern is the typo mentioned

[isabelle-dr]

Thanks, @emmambd! I fixed the typo, merging this PR