Add Default Initial Branch Name for Repositories Group Setting

What does this MR do?

For #221014

Adds the ability for group admins to change the default initial branch name for new repositories in that group.



Does this MR meet the acceptance criteria?


Availability and Testing


If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

  • [-] Label as security and @ mention @gitlab-com/gl-security/appsec
  • [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
  • [-] Security reports checked/validated by a reviewer from the AppSec team
Edited by Thomas Randolph