Add a way to remove users on the hunters list page

[welkin25]

I think there should be a "remove" button next to promote/demote to let operators remove users from a team.

Use cases

• user quitting the team
• if I want to use JR for my friends but I don't participate myself, I can set up JR, invite them and then remove myself.

[ebroder]

Yeah this has come up for us, too. Beyond just removing them from the hunt, we also need to think about undoing some of the side effects as well (Discord groups, Drive access, etc.). But it seems worth doing

[zarvox]

In addition to external access, we should think about how to handle artifacts left by users that are no longer actively attached to a hunt, like chat messages they've sent, or guesses they may have submitted -- we should be sure that we cleanly handle the cases where we have no profile/display name information for the value of some object's createdBy or updatedBy fields.

[ebroder]

If we had a good strategy for that it would get us most of the way to solving the hard parts of #296 too

[ebroder]

Having thought about this a little bit, this does have a key difference from #296, although there's potentially still room to use some shared infrastructure. If we assume that for #296 we're going to do a backfill migration to update createdBy etc. on existing records (which is at least what I'm assuming), then we don't have a long-term problem of records that reference users that no longer exist. That's not true here (or at least, even if the users don't exist, they aren't visible to things like displayNames), and merging users does still have the short-term problem.

One option is to add a formerHunts: string[] to user records. When a user is removed from a hunt, we move the hunt ID from u.hunts to u.formerHunts. Then we update displayNames (and probably also avatars) to fetch users with both set. They wouldn't show up anywhere else (since everything else would query MeteorUsers.find({ hunts: huntId }).

(When we merge two users together, I think we end up moving the "merge-from" user's hunts over to formerHunts, at least until we've finished the cleanup job, at which point we can just delete them)

[ebroder]

As an update to this from discussion on #2804, rather than introduce a formerHunts property on users (such that users remain visible after they're removed), we probably instead want a separate tombstone collection for "former hunters" that captures their display name (and maybe some other profile properties) at the time they were removed.