Add blue border to buttons on focus

It was decided in the discussion for #21287 (moved) that we should add the Bootstrap blue glow for focus state to all buttons in GitLab. This should be applied to all buttons, including award emoji buttons, dropdowns, the tabs in the nav bars, etc.

Mentioned in issue #24063 (moved)

I guess this is just a matter of reverting to the original bootstrap style, as seen on their focused form inputs.

@pedroms Exactly, I imagine it shouldn't take too much effort. I'll add the ~up-for-grabs label.

Added ~131895 label

Reassigned to @tauriedavis

Mentioned in merge request !7347 (merged)

Status changed to closed by merge request !7347 (merged)

added ~1434245 label

mentioned in issue gitlab#6851