Use `leave_room` in `leave_all_rooms`

WIP: Add command to delete a list of users
also implements a flag to prevent the user from being removed from their joined rooms.

Report user deactivation failure reason

Don't send leave events by default when mass deactivating user accounts

Don't stop leaving rooms if an error was encountered

WIP: Rename command, make flags consistent, don't deactivate admin accounts.
Accounts should be deactivated as fast as possible and removing users from joined groups is completed afterwards.

Fix admin safety logic, improve command output

Continue leaving rooms if a room_id is invalid

Ignore errors from leave_room

Add notice to the list-local-users command
Output form list-local-users can be used directly without modification with the deactivate-all command

Only get mutex lock for admin room when sending message

Doc rendering is exactly as before, but it now actually tests the code

Prevents the server from crashing/become unresponsive when overly long
messages are sent