Update dev-2.0 docs with recently-added contributors and stewards

[ksen0]

To support 2.x patch/minor release process, the README, stewards and contributors lists in the 2.0 branch should reflect the main branch, as there is no branch-level distinction. In this instance, the updated steward guidelines are also included, though in general the contributor guidelines can and will diverge (for example, testing has already diverged).

This PR contains:

git checkout main -- README.md stewards.yml contributor_docs/steward_guidelines.md .all-contributorsrc

Previous iteration: #7731

In general, a more robust cherrypicking from main to 2.0 in both website and this repository is needed. However, not all updates are equally applicable or cherrypickable. At the moment, I'm doing this copy manually to make sure it makes sense, but copying over README.md stewards.yml .all-contributorsrc could be automated.

PR Checklist

• npm run lint passes
• Inline reference is included / updated
• Unit tests are included / updated