Update project star/unstar tooltip

## What does this MR do?
Fixes project toggle star button tooltip to show actual tooltip for its state.

## Are there points in the code the reviewer needs to double check?
No.

## Why was this MR needed?
- When you star a project tooltip wasn't changing.
- When you star a project and refresh the page, tooltip was still showing `Star Project`

## What are the relevant issue numbers?
Fixes #18143

## Screenshots (if relevant)

### Before 
![Screen_Shot_2016-06-15_at_15.31.57](/uploads/e005951c23eeed7c2761a0ec1911f3ce/Screen_Shot_2016-06-15_at_15.31.57.png)

### After
![tooltip-change](/uploads/4caec99eac6ffcc7331947fdfdb9e051/tooltip-change.gif)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- [ ] Tests
  - [ ] Added for this feature/bug
  - [ ] 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 !4672