MSC4171 Omit service members from room summary

[Half-Shot]

For #17859

This applies the rules for MSC4171 to the m.heroes response in sync. For clarity, this PR is needed to fix behaviors in some modern clients such as EX which use heroes to determine room names rather than local calculation.

MSC discussion for excluding service members from m.heroes: https://github.com/matrix-org/matrix-spec-proposals/pull/4171#discussion_r1688649042

Pull Request Checklist

• [x] Pull request is based on the develop branch
• [x] Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
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• [x] Code style is correct (run the linters)

[Half-Shot]

I think on balance and after talking to @erikjohnston, we have the ability to do this filtering in the client and it sounds trivial to do so from both v2 and sliding sync. Let's do that, and if that ends up being annoying then we can circle back to a backend implementation.