Preload rich viewer

What does this MR do and why?

Preloads the rich viewer in order to improve LCP

Screenshots or screen recordings

before	after
Rich viewer is loaded towards the end of the lifecycle	Rich viewer is (pre)loaded the the beginning of the lifecycle

How to set up and validate locally

View a markdown file.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #331447