Notify CI/CD users about keyword deprecations in GitLab UI
This issue is a follow-up from discussions in #238388 (comment 550365887).
Keyword deprecation can break your pipeline, and currently we don't notify our users about it except for the release post.
Explore ways to notify the engineers responsible for maintaining CI/CD configuration about any planned deprecation. We should also provide help with replacing the old keywords with the new syntax.
A long-term goal could be to provide a suggestion that can be easily applied to the config which would upgrade your CI/CD config with new syntax.