Alert in Slack when review app checks fail

Context

Closes https://gitlab.com/gitlab-org/quality/engineering-productivity-infrastructure/-/issues/38

In !104595 (merged), we have introduced two jobs that report on GKE resource count and GCP quotas.

We would like to receive an alert when those fail.

Additionally, we would like to receive a notification in Slack when the review-cleanup job fails.

From Draft to Ready

• Drop this commit: 1f8cb19d

What does this MR do and why?

Adds slack notifications for the following three events:

• A command in the script part of the review-cleanup job fails
• A command in the script part of the review-k8s-resources-count-checks job fails
• A command in the script part of the review-gcp-quotas-checks job fails

How was it tested?

I added this commit to the MR: 1f8cb19d

The results are in the section below.

Screenshots or screen recordings

(the reaction emojis and threads are not part of this MR 😆 )

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.