Fix filter label tooltip HTML rendering

## What does this MR do?
Tooltips on labels used in a filter are now rendered as HTML

## Are there points in the code the reviewer needs to double check?
Shouldn't be

## Why was this MR needed?
Fix existing bug (See screenshot below for reference)

## What are the relevant issue numbers?
Closes #20592 

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-08-04_at_10.27.59_AM__2_](/uploads/7ca37d4116f15a2d22ad16fbbe682f1f/Screen_Shot_2016-08-04_at_10.27.59_AM__2_.png)

After:
![Screen_Shot_2016-08-04_at_10.24.37_AM__2_](/uploads/7fce6c8a93d293767dacbcd682831f86/Screen_Shot_2016-08-04_at_10.24.37_AM__2_.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5671