Add maintenance notes in runner view

What does this MR do and why?

This change adds maintenance notes in the runner details page.

Changelog: added EE: true

Related to #348299 (closed)

Screenshots or screen recordings

view	update

How to set up and validate locally

1. Ensure you have an GitLab Ultimate license.
2. At least one runner must be registered.
3. Visit the Admin -> Runners page.
4. Update a runner with a new Maintenance Note.
5. Check the information is displayed.

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.