[FE] Set user availability - Add busy indicator to sidebar

Broken down from #259649 (closed)

Let's add the busy indicator to the the following elements when a user has ticked the busy checkbox:

e. Sidebar popover f. Sidebar dropdown g. User comment
CleanShot_2020-10-15_at_17.01.01 CleanShot_2020-10-15_at_17.01.16 CleanShot_2020-10-15_at_17.03.54

Expected outcomes

  • Busy status available in issues sidebar
  • Busy status available in the MR sidebar
Edited by Ezekiel Kigbo