Issues for KDE migration to Gitlab

See #53206 (moved) for the preface, this issue is the meant as tracker to list the issues affecting KDE. I will update the list with issues we're getting affected.

Blocker issues

• Support for multiple project boards : #53811 (closed)
• Support for merge request approvals in CE #42096 (moved)
• Ability to invite users to a confidential issue: #41973 (moved) and #40545 (moved)
• Port Merge Request Reviews from GitLab EE to GitLab CE : #60690 (moved)

Would be nice to have

• Add project configuration option to require MRs to have the allow_collaboration flag set #55661 (moved)
• Blocker/sub-task/parent task tracking support for Issues : #64186 (moved)