Update GitLab Shell to v12.1.0

What does this MR do?

See gitlab-shell!372 (merged) for more information on what changed in GitLab Shell.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content