Update release notes, changesets, and presence README

[tylerbutler]

• Updates the presence grouping changeset and the README to match and consistently use the term grouping.
• Updates the events tree change to be a changelog-only change and not include it in the release notes. Since it's an internal reorganization I think this is OK.
• Regenerated the release notes with the previous changes.

[github-actions]

🔗 No broken links found! ✅

Your attention to detail is admirable.

linkcheck output

> [email protected] ci:check-links /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test "npm run serve -- --no-open" 3000 check-links

1: starting server using command "npm run serve -- --no-open"
and when url "[ 'http://127.0.0.1:3000' ]" is responding with HTTP status code 200
running tests using command "npm run check-links"


> [email protected] serve
> docusaurus serve --no-open

[SUCCESS] Serving "build" directory at: http://localhost:3000/

> [email protected] check-links
> linkcheck http://localhost:3000 --skip-file skipped-urls.txt

Crawling...

Stats:
  170006 links
    1595 destination URLs
    1825 URLs ignored
       0 warnings
       0 errors