Use NotesFinder#target to find Epics

The following discussion from !13265 (merged) should be addressed:

• @felipe_artur started a discussion: (+4 comments)

  I think we should also make NotesFinder#target be able to return epics here, but that would require an EE module for it.

  Maybe it is out of the scope for this merge request.

So we should:

Override NotesFinder#target so it is able to find epics.

Evaluate refactoring of the discussed code part (is it needed after using NotesFinder#target for epics?)