Manage archived spaces

[strugee]

Acceptance criteria:

• plan.yaml has a list of archived spaces.
• For any archived space in plan.yaml:
  • Patch moves the conference space to a config-specified archive space (see Decommission Matrix spaces of past conferences organization#362 (comment)). Then:
  • Patch recursively applies the power level changes specified in Decommission Matrix spaces of past conferences organization#362 (comment) to all rooms in the space, in the reconciler.
• Power level reconciliation, based on plan.yaml's inheritUserPowerLevels key, does not take place in any archived space.

[strugee]

Related, because it fixes the volunteer onboarding ACL problem we were having: b6db221