Update weekly meeting agenda to direct topic suggestions and add housekeeping time (#3522)

* Remove old backlog agenda and unused tag filters from weekly meeting agenda, add housekeeping entry

* Update agenda.md

Building on Lorna's work, this:
- changes housekeeping to governance to avoid conflict with the issue label
- tightens up the instructions (wordsmithing and general cleanup)
- re-orders meeting info and CoC
- shortens the ideal time for the first two items to 5 mins

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Co-authored-by: Marsh Gardiner <marsh.gardiner@gmail.com>