create and publish gitlab-operator Helm chart to replace kustomize

Summary

This MR adds and publishes the gitlab-operator as a Helm chart. It also deprecates Kustomize except for building the test custom resource.

Related Issues

• Closes #481 (closed)
• Closes #602 (closed)
• Relates to #307

Acceptance Criteria

• published kubernetes manifest is fully compatible with existing one
• pipeline is green
• ability to deploy multiple instances in CI safely
  • confirm there's no ValidatingWebhookConfiguration collisions ( #602 (closed) )

Testing

diff manifests

(using dyff and kubernetes-split-yaml

make build_operator
curl -O https://gitlab.com/api/v4/projects/18899486/packages/generic/gitlab-operator/0.5.1/gitlab-operator-kubernetes-0.5.1.yaml
mkdir -p manifests/{gl-k8s,gl-helm}
kubernetes-split-yaml --outdir manifests/gl-helm .build/operator.yaml
kubernetes-split-yaml --outdir manifests/gl-k8s gitlab-operator-kubernetes-0.5.1.yaml
dyff between manifests/gl-k8s manifests/gl-helm 

same thing for openshift variation:

make build_openshift_operator
curl -O https://gitlab.com/api/v4/projects/18899486/packages/generic/gitlab-operator/0.5.1/gitlab-operator-openshift-0.5.1.yaml
mkdir -p manifests/{ocp-gl-k8s,ocp-gl-helm}
kubernetes-split-yaml --outdir manifests/ocp-gl-helm .build/operator-openshift.yaml
kubernetes-split-yaml --outdir manifests/ocp-gl-k8s gitlab-operator-openshift-0.5.1.yaml
dyff between manifests/ocp-gl-k8s manifests/ocp-gl-helm 

pipeline

create integration branch for the MR (for example 481-gitlab-operator-helm-XX)

git pull
git fetch "git@gitlab.com:boxboat/gitlab-operator.git" 'helm'
git checkout -b 'boxboat/gitlab-operator-helm' FETCH_HEAD
git branch 481-gitlab-operator-helm-XX master
git checkout 481-gitlab-operator-helm-XX
git merge --no-ff 'boxboat/gitlab-operator-helm'
git push origin 481-gitlab-operator-helm-XX

pipeline will be automatically triggered.

multiple pipelines

repeat the process from pipeline section above with another branch name and confirm both are working properly.