What does this MR do?
This monkey patches
Redis#keys in the specs to raise an error.
That way we can avoid using it in production.
Why was this MR needed?
As @andrewn explained in https://gitlab.com/gitlab-org/gitlab-ce/issues/37383#note_43252534,
KEYS iterates over each key in redis.
Does this MR meet the acceptance criteria?
Changelog entry added, if necessary
Tests added for this feature/bug
Has been reviewed by Backend
What are the relevant issue numbers?
This is needed as a step to make the Circuitbreaker production ready: #37383 (closed)