Feature request: admins to have the ability to "close" a thread

[smoya]

Sometimes, threads can blow out or go out of control 🔥 . Slack doesn't have the future for not allowing more people to write in a thread but maybe Candebot could help by adding a new action on message threads where admins can set a thread as closed, so Candebot removes any new message posted in there from that time, adding a ephemeral message (only visible to the user) saying the thread is closed.

For this, we would need a DB to store the state.