<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=213235) </details> <!--IssueSummary end--> Extract some of the logic from `lib/gitlab/bitbucket_import/importer.rb` as per https://gitlab.com/gitlab-org/gitlab/-/merge_requests/27524#note_315221527 suggestion to create better abstractions. Object creation can be split into separate Creator classes (Issue, MR, etc)