Update/clarify the WordPress Object Cache Pro documentation

[jkudish]

Summary

Update + clarify the WordPress Object Cache Pro documentation to explain that certain steps of the setup can only be performed on development or multidev environments.

Additionally, add a warning about the health check notice that is expected to pop up

Release:

• [ ] When ready

---

Post Launch

Do not remove - To be completed by the docs team upon merge:

• ~Redirect /old-path/ => /new-path/ (if applicable)~
• ~Include/exclude pages ^ respectively within docs search service provider (if applicable)~
• [ ] For Heroes - add a props post to the discussion board.
• [ ] Remove from the project board