git-init: do not assume master as default branch

[vdemeester]

As of today, when the user doesn't specific a revision (branch, commit, …), we are defaulting to master. There is some problems with that: master might not be present on the remote. The recent wave of change of default branches on several project, including https:/spring-projects/spring-petclinic are putting this problem into light : see tektoncd/catalog#365.

Instead of making the assumption that we should use master when the revision is empty, we should inspect the remote. git can give us this information.

$ git remote show origin
* remote origin
  Fetch URL: https:/spring-projects/spring-petclinic
  Push  URL: https:/spring-projects/spring-petclinic
  HEAD branch: main
  Remote branches:
    gh-pages  new (next fetch will store in remotes/origin)
    main      new (next fetch will store in remotes/origin)
    wavefront new (next fetch will store in remotes/origin)

After doing the git init and adding the remote git remote add origin …, we should get the default branch (remote HEAD) if the revision isn't specified. The way to do it should be as simple as git symbolic-ref refs/remotes/origin/HEAD 👼

/kind bug

[vinamra28]

/assign