Summary

Have the ability to single-select epic in the backlog.
Currently, when selecting an epic, instead of it being single select, it ends up selecting issues related to previously selected epic and this epic. As a result, you need to manually unselect the previous epic.

Steps to reproduce

1. Go to the backlog
2. Enable epic panel
3. Select an epic then select another one

Expected behaviour

It should act as single-select, instead, it acts as muti-select