Move gitlab Helm chart to its own argocd app

The following discussion from !4 (merged) should be addressed:

• @alossent started a discussion: (+2 comments)

  Binary file chart/charts/gitlab-4.11.5.tgz must be removed and gitignored

  Also related chart.lock

• OK, no problem: the repository secret can be created by this Helm chart, you just need to explicitly create it in the openshift-cern-argocd namespace (maybe include the release name in the secret name, to avoid collisions). Or create the secret in okd4-install and make it clear in this project's README that there is this requirement to deploy it with ArgoCD.

• Set nodeSelector for gitlab-pages pod to node-role.kubernetes.io/standard: ""

Not critical, this can be done as a follow-up and keep the binary for now.