Support for component projects in QA issues

Related to gitlab-com/gl-infra/delivery#841 (closed)

This adds Gitaly merge requests to QA issues, behind a qa_multi_project feature flag.

Also includes minor refactoring to the Qa::Ref class:

• Renames should_be_converted? to include_suffix? to be more descriptive of how it's actually used
• Use String#match? since we don't need the MatchData objects.
• Ensure ref is not an auto-deploy tag in tag?, since it previously returned true, even though these tags aren't suffixed.

Adding additional projects such as Workhorse will take additional work, because we reference them as semver strings, which aren't Git references, and we'll need to conditionally add the v prefix in order to get a valid reference.