Get the tests deterministic or bust!

Also, explain what the constants are doing and why. And don’t output the log message if it doesn’t apply.

This code should not break other tests because the rate limits are off by default.

Set 0.69.0 instead of latest for codeclimate image

See merge request gitlab-org/gitlab-ce!15445

Refactor  Cluster docs

Closes #39952

See merge request gitlab-org/gitlab-ce!15418