Add a description text field to environment details

What does this MR do and why?

This MR adds a markdown editor for the environment description. It is based on the backend and database changes from the related MR.

The markdown field is shown on the new and edit pages.
The rendered markup is then shown on the environment details page. We truncate the description to 3 lines (default) with the Read more button.

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

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Description	Screenshot
Edit/new environment
Less than 3 lines
More than 3 lines
More than 3 lines

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Go to the project -> Operate -> Environments
2. Create an environment.
3. On the create form verify the description field.
4. Save and verify how the description is rendered on the details page.
5. Edit the environment and verify the changes.

Related to #450944 (closed)