MatrixRTC server client clock sync.

[toger5]

MSC4094

Checklist

• Tests written for new code (and old code if feasible)
• Linter and other CI checks pass
• Sign-off given on the changes (see CONTRIBUTING.md)

---

This PR currently has none of the required changelog labels.

A reviewer can add one of: T-Deprecation, T-Enhancement, T-Defect, T-Task to indicate what type of change this is, or add Type: [enhancement/defect/task] to the description and I'll add them for you.

[toger5]

This is sth that might be helpful for other scenarios as well but as of now we found a different solution for the problem this tried to help with (reliable call memberships)