Add support for description field to organizations

What does this MR do and why?

Related to #435536 (closed)
Designs - #410343 (closed)

The grouptenant scale team is starting to build out an Organization MVC. For more information about what an "Organization" will be see https://docs.gitlab.com/ee/architecture/blueprints/organization/

This MR adds a description field when creating/editing an organization.

Notes for reviewers

• Organization descriptions support markdown so I used a markdown editor instead of a basic textarea.
• Organizations are still in early stage of development so there is still some mock data being used. If the data shown in the UI doesn't make sense it is most likely mock data.
• There is a bugux with the slide animation on the settings page. I have #436419 (closed) open to fix this.

MR acceptance checklist

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Screenshots or screen recordings

Screen_Recording_2024-01-02_at_5.04.05_PM

How to set up and validate locally

1. Open the rails console
   • bin/rails console
2. Enable the :ui_for_organizations feature flag
   • Feature.enable(:ui_for_organizations)
3. Navigate to /-/organizations/new
4. Fill out the form and add a description
5. Navigate to Settings -> General
6. Edit description and click Save changes