Fix suggested colors options for new labels in the admin area

## What does this MR do?

Execute the JS related to the suggested colors options when user access the new label in the admin area.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

Clicking in a suggested color when creating a new label in the admin area don't change the background color.

## Screenshots (if relevant)

* Before

    ![2016-08-31_19.56.14](/uploads/3d50236dac578910c5062aa1e83da350/2016-08-31_19.56.14.gif)

* After

    ![2016-08-31_19.58.59](/uploads/376ffdcbb5b80ef51ab1d642fe9486d0/2016-08-31_19.58.59.gif)

## Does this MR meet the acceptance criteria?

- [X] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry 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)
- [ ] 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)

## What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/21726

See merge request !6138