Merge branch '19184-turn-off-autocomplete-on-label-dropdown-for-issues-mr-s' into 'master'

Disabled native autocomplete for dropdown filter inputs

## What does this MR do?

Disables native autocomplete for the dropdown filter inputs.

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

Did we want this on all dropdown filter inputs? The issue specifies only the 'label' filter input but I think it is relevant for any filter input?

## Why was this MR needed?

No need for native autocomplete.

## What are the relevant issue numbers?

Closes #19184

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [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 !4974