Initial draft for the moderation policy

This was written today with @albakham, as an attempt to build a formal moderation policy for the community spaces. You can comment directly on the draft and suggest any addition/modification.

This will remain open at least a few day to ensure we can gather as much feedback as possible before adopting this document as our moderation policy.

You can view the rendered document here: https://code.eliotberriot.com/funkwhale/governance/blob/e619c0ae211e47b15135b8005f4ed3dd60dee7cf/MODERATION.md