Add review-delete-deployment to review-apps failed notifications

Context

Related to gitlab-org/gitlab#431870 (closed).

What does this MR do and why?

Add review-delete-deployment to notifications

We want to be informed when this job fails, as it blocks the review-apps deployment as much as a failed review-deploy job.

It will be useful to understand what blocked a namespace from being deleted, and fix the root cause, if we can do this at all.

How many notifications will this create?

See https://app.periscopedata.com/app/gitlab/1156857/David-Dieulivol---EP-playground?widget=17445549&udv=1948533 for a detailed answer.

We have a success rate above 96% in the last few months, so we shouldn't get too many.

Action items

• If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review