Update Rename Worker docs
### Why Regarding the [rename worker classes process](https://docs.gitlab.com/ee/development/sidekiq/compatibility_across_updates.html#renaming-worker-classes), by adding a small bit of further guidance, we can improve engineers' ability to get through this task with more certainty and greater efficiency. ### What Add to docs - [ ] type of FF to use - [ ] where to use the FF - [ ] brief explanation and/or diagram of why this matters from a deployment perspective
issue