Use rich text editor in snippets description

What does this MR do and why?

Enable use of the rich text editor when editing/creating the snippet description.

This is part of the Make Available Rich Text Editor Across GitLab (&7098) Epic.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After

How to set up and validate locally

Create or edit the description of a snippet and verify the rich text editor can be used.