Add simple identifier to public SSH keys ## What does this MR do? Adds a simple identifier of user_name + hostname to public SSH keys ## Are there points in the code the reviewer needs to double check? ## Why was this MR needed? To help people identify keys when they export them ## What are the relevant issue numbers? #18866 ## Screenshots (if relevant) ## 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 - [ 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) Closes #18866 See merge request !5614