[EuiCodeEditor & EuiCodeBlock] Recommendations and migration guidance

[chandlerprall]

EuiCodeEditor is now deprecated and will be removed in a future version of EUI

• If you just want to represent a more or less static code snippet (max length around 15 lines) use EuiCodeBlock.
• If you need capabilities to edit, or want to print longer code (or potentially don't know how long, because you're printing JSON from APIs), use CodeEditor (within Kibana).
• Don't use EuiCodeEditor for new places more, and instead favor implementing a Monaco editor like CodeEditor.

Originally posted by @timroes in elastic/kibana#71425

[thompsongl]

#5323 removed EuiCodeEditor and the docs have recommendations in place