Epic Activity Feed Order

Problem to solve

We now have the ability to sort an issue or MRs activity to "newest first". See #14588 (closed). Epics do not have this capability which breaks your mental model if you regularly transition between Epics and Issues.

Proposal

Follow the same pattern in #14588 (closed) and add the ability for a user to sort the discussion order based on Newest first or Oldest first (current).