Epics: the widgets should allow searching for the epic number

Proposal

When you are trying to assign an epic to an issue, you likely know the epic number you want to assign, but there is no way to do that through the epic widget that is accessible through the right-side bar.

See screenshot below:

The current workaround is to use slash commands. I believe querying with the epic number should work as well as querying for the epic title we do today.