Bugzilla Integration ## What does this MR do? Adds Bugzilla as a project service for external issue tracking ## Are there points in the code the reviewer needs to double check? ## Why was this MR needed? Provides a notable Bugzilla option for use as an external issue tracker. Existing Custom Issue tracker can be used to setup Bugzilla but this makes it clear that Bugzilla is an option. ## What are the relevant issue numbers? Closes #14669 ## Screenshots (if relevant) ## Does this MR meet the acceptance criteria? - [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added - [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md) - [ ] API support added - Tests - [x] Added for this feature/bug - [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 !4930
