Set default branch to 2.x or provide administer maintainers permission

Problem/Motivation

@amarincolas: Only you have permission to set the default branch in GitLab because it needs "Administer maintainers" permission!

Could you please change the default branch to 2.x or give the permissions to us active maintainers?

Thank you!

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes