Find a way to auto-close/hide DMs

[dblock]

The group DMs are accumulating...

[orta]

Perhaps there could be a private chat per lead? On a new sup it gets wiped and new people are added?

e.g. #sup-lead-orta is used because I'm assigned to setup the meeting, it wipes the history and, removes anyone old, and adds 2 people. Then later it's re-used.

[dblock]

We use mpim_open which can't do that. We just need to call mpim_close on older DMs.