From now on, only match on the annotations, instead of falling back to
legacy app label. This enables users to use the app label for other
purposes such as helm charts.
Having an invalid KUBECONFIG without a token in it is not helpful. This
only became possible recently now that we are creating a separate
namespace and service account (and hence token) to send to the runners.
This led to somewhat surprising results when troubleshooting
https://gitlab.com/gitlab-org/gitlab-ce/issues/53879 as I found that the
KUBECONFIG was still being passed but KUBE_TOKEN was not. These things
really should have been linked.
Furthermore now that we are also using the [presence of KUBECONFIG to
decide whether or not to run build steps in Auto
DevOps](294d15be3e/lib/gitlab/ci/templates/Auto-DevOps.gitlab-ci.yml (L164))
I think it makes even more sense to ensure that KUBECONFIG is a complete
config if passed to a job.
