Add kube-janitor annotation

What does this MR do?

To make sure buildx agents are properly cleaned up after use and prevent premature agent removal - add appropriate annotation to namespace indicating intent to use agent for the next 6 hours.

Related issues

• related to Configure CNG build scripts to allow multi-arch... (gitlab-org/distribution/team-tasks#1142 - closed) • Dmytro Makovey • 16.6 • At risk
• related to [CI] [Spike] Investigate use of kube-janitor fo... (gitlab-org/distribution/team-tasks#1263 - closed) • Dmytro Makovey • 16.9
• related to https://gitlab.com/gitlab-org/distribution/infrastructure/kubernetes-provisioning/-/issues/29+s

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated
• New dependencies are managed with dependencies.io

Testing

• (re)run any of the jobs from pipeline building images. buildx pods will bet instantiated in buildx cluster under the namespace corresponding to CI_COMMIT_REF_SLUG
• inspect the created pods:

  k get -o json namespace build-buildx-kube-janitor | jq .metadata.annotations

  output should look like:

  {
    "janitor/expires": "2023-11-14T22:21"
  }

• re-running any of the build jobs from the pipeline should bump above annotation expiration time correspondingly