Change docs review and cleanup jobs to same CI stage

What does this MR do?

Having the docs-review jobs in different stages causes the environments to not be cleaned up. See screenshot below, and check out https://docs.gitlab.com/ee/ci/yaml/README.html#environmentaction:

The "stop_review_app" job is required to have the following keywords defined:

• when - reference
• environment:name
• environment:action
• stage should be the same as the review_app in order for the environment to stop automatically when the branch is deleted

This MR renames the cleanup stage to review, and puts both docs-review jobs in there so that they will be automatically cleaned up, as per the link above.

I am not sure what is the best way to remove all these stale docs review environments, but I would assume someone should make a script to clean them all out in one go?

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?