Add groups stuff to spec

[richvdh]

Proposal, API summary, semi-accurate API details
Author: @erikjohnston

[richvdh]

Also m.room.related_groups, which doesn't seem to be in the google doc

Edit: related_groups is MSC1214

[non-Jedi]

Would be really helpful on this one to have some indication (even if in a comment afterward) on how those three docs relate to each other.

So for anyone else following after me, here's my best summary:

1. Overall description of groups api.
2. List of all groups api endpoints without details or description.
3. Detailed descriptions of api endpoints.

[richvdh]

This has been in production for over a year, so it's a bit late to be arguing about the proposal now. Which sucks, but here we are.

[ara4n]

i'm not so sure. the current system in production has a lot of issues, and i at least am worried about speccing them into concrete in the current API shape, at least until we've decided what the medium/long-term plan is here.

[ptman]

#1772

[turt2live]

I'm declaring this as obsolete now that MSC1772 (Spaces, or Communities v2, or Groups v2) is in FCP. We anticipate that Spaces will take over the spec, and that Groups will never make it into an official spec document.