Cleanup namespaces created for environments on environment-elimination

Problem to solve

Once https://gitlab.com/gitlab-org/gitlab-ce/issues/52494 is complete, a dedicated namespace will be created for each environment that is created. When the environment is eliminated, the corresponding namespace will remain.

Further details

Proposal

When an environment is destroyed so should the corresponding namespace be destroyed.

In order to make this configurable by the user, we want to add a new option delete_namespace to <job>.environment.kubernetes. Using the environment.on_stop feature, deleting namespaces could be achieved by two jobs and a cluster with a * environment scope to deploy the review app:

review_app:
  script: deploy-review-app
  environment:
    name: review/$CI_COMMIT_REF_NAME
    on_stop: stop_review

stop_review:
  environment:
    action: stop
    kubernetes:
      delete_namespace: true

Permissions and Security

Documentation

What does success look like, and how can we measure that?

Links / references