Header search bar scope highlight

I added a new way to highlight the current search scope in the header search bar.

When searching within a context (inside a group or project) new search UI. Will offer easily recognizable context visual cues inside the expanded search bar itself.

closes issue: #284139 (closed)

before	after

Steps to reproduce:

1. check out this branch
2. search via header search bar
3. if searching with no context (not inside project or group) you should see marking saying "in all Gitlab"
4. if searching with the context you should see context highlight inside the search bar.