For large accounts with huge volumes of messages, it can be very
wasteful to make the meta request so often. It also puts un-necessary
load on the DB bombarding it with so many requests. This PR fixes it by
throttling the requests to 5 seconds for all users with more than 1000
accessible chats.
### Why not cache this value in the backend?
Well, it's a bit tricky, since a user can have different permissions
over inboxes and can see different chats, maintaining a cache for each
of them is not effective, besides the requests will reach the server
anyway.
