This is primarily a feature for onboarding, where an organization
administrator might send a bunch of random test messages as part of
joining, but then want a pristine organization when their users later
join.
But it can theoretically be used for other use cases (e.g. for
moderation or removing threads that are problematic in some way).
Tweaked by tabbott to handle corner cases with
is_history_public_to_subscribers.
Fixes#10912.
The first menu option supported is to narrow to the topic.
The chevron only shows up if you turn on feature_flags.muting.
(imported from commit 17482f538a6d3e4ff96a36c042bad972d34f4b11)
kunal-mohta
Aditya Bansal
Steve Howell
Umair Khan
Preston Hansen
Steve Howell