The goal of this issue is to indicate to users whether their Segments are used in other scheduled reports and how many.
- display in the "Edit Segment" screen how many Scheduled Reports are currently set to use this segment. If no scheduled reports use this segment KISS: do not display anything.
- add the counter to the Segments API response
- could we make this show up in one of Segment editor screenshot test?
Idea coming from #5226