Make it possible to erase build content (artifacts, trace)
This feature makes it possible to remove build content - build artifacts and build traces.
- [x] Remove artifacts
- [x] Remove metadata
- [x] Remove build traces
- [x] Wait for https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/1942 this to be merged
- [x] Fix the permissions after the merge
Closes#3421
See merge request !2560