[Hermes Init]: Use mainline branch of CI templates repository

hermes init uses the https://github.com/softwarepub/ci-templates to pull its CI templates. Currently, the branch `feature/init-custom-ci` is used. We should change this to `main` and adapt the change process in the template repository accordingly.

Note: This may only be implemented after https://github.com/softwarepub/ci-templates/pull/14 is merged.