Bump @ng-select/ng-select from 14.5.6 to 14.6.0 in /frontend

Bumps [@ng-select/ng-select](https://github.com/ng-select/ng-select) from 14.5.6 to 14.6.0.
- [Release notes](https://github.com/ng-select/ng-select/releases)
- [Changelog](https://github.com/ng-select/ng-select/blob/master/CHANGELOG.md)
- [Commits](ng-select/ng-select@v14.5.6...v14.6.0)

---
updated-dependencies:
- dependency-name: "@ng-select/ng-select"
  dependency-version: 14.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]