Update UI naming guidelines to match new Kibana chrome #4073
Description
Kibana is evolving and we need to refresh our "Writing about the UI" (elastic-only access at this time) guidelines. This is the opportunity to revise especially the following:
- Screenshot guidance
- Naming section
- Check if the rest is still accurate and/or actually needed. Some content might be better positioned outside of this section as it's not that specific to writing about the UI.
When this is done, these guidelines should be added to our public writing docs like in #4060 for example