Proper handling of projects where the main branch is not called 'master'

[ciyer]

Description

Renku should work correctly on repos where the main branch is not called 'master'.

[ciyer]

Some notes

• git clone will checkout the branch marked as "default" in GitLab.
• In the core service, it should be possible to just rely on the default behavior of git for ensuring we are on the default branch
• As with git, it should be possible to set the name of the initial branch when creating a project, using --initial-branch in the CLI, or as an argument to the core service
• The UI should look up in GitLab the default branch name for the group when creating a new project and pass that to ensure consistency.

See Also

• https://github.com/github/renaming
• https://sfconservancy.org/news/2020/jun/23/gitbranchname/
• https://docs.gitlab.com/ee/user/group/#use-a-custom-name-for-the-initial-branch
• https://git-scm.com/docs/git-init#Documentation/git-init.txt---initial-branchltbranch-namegt

Testing

These projects can serve as test cases

• https://dev.renku.ch/projects/cramakri/main-as-main
• https://dev.renku.ch/projects/cramakri/main-as-main-with-master