Add an ephemeral message in chat when new snapshots have been pushed

[fuzyll]

What is the feature you'd like to have?
When the client realizes that new snapshots are available, a message in Chat View should appear that says something like:

N snapshots from <user> are now available to pull

If there are snapshots from multiple users, I'd just print multiple lines. These lines should be in a neutral color (e.g. light-to-medium gray) to distinguish them from 'actual' chat messages.

Also, I don't believe it should be necessary (or desired) to have these messages saved into the database (like we do for regular chat history in Enterprise).

Is your feature request related to a problem?
Additional ways to signpost to users that additional snapshots are available are always good.

Are any alternative solutions acceptable?
Possibly, but this should be the quickest and easiest to implement of the ones we've discussed.

Additional Information:
Issue was migrated here from the internal Enterprise issue tracker.