Create new repositories on the main branch

[clementbiron]

The versions, snapshots and tracking-results repositories created by the engine got the default branch of the Git configuration of the server, master on most servers, whereas the deployment clones them on main and the reporter links to blob/main. Once published, such a repository pushed a master branch next to the main branch that GitHub creates with the README.

New repositories are now created with git init --initial-branch=main, which requires Git 2.28, available on all the operating systems the engine is guaranteed to work on. Git ignores this option for existing repositories, which keep their branch, as renaming it would diverge from their remote; the changelog explains how to move one to main.

[Ndpnt]

I agree with the change. I would frame the motivation differently though: the point is less that the deployment expects main (it could be made configurable) than that main is now the default everywhere the engine publishes. GitHub and GitLab create main by default, the deployment already assume it, and Git's own roadmap states that Git 3.0 will create new repositories on main to match the forges. The engine was the last piece whose result still depended on the local Git configuration of the server. Framed this way, a constant rather than a configuration option is the obvious choice.