Resolve "GitLab Migration - Migrate CI Pipelines"

What does this MR do and why?

This feature is part of the new Project Migration feature which directly migrates projects between Gitlab instances. It is currently enabled with the bulk_import_projects feature flag. This MR adds Ci::Pipeline migration to any existing project migration

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

1. Feature.enable(:bulk_import)
2. Feature.enable(:bulk_import_projects)
3. Create a top level group and project in it
4. Create a CI Pipeline in the new project
5. Run the pipeline
6. Go to /groups/new#import-group-pane page and enter instance url and access token (needs to be api and read_repository scope)
7. Select newly created group and click Import
8. Wait for Group import to complete and verify imported project's pipelines and builds (build logs not imported yet see #345268 (closed))

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #339407 (closed)