Show edited at for task descriptions

What does this MR do and why?

Add Edited by section to Task description - #365998 (closed)

Screenshots or screen recordings

On hover

How to set up and validate locally

1. Visit an issue page
2. In the gray box for 'Tasks', click Add to add a new task. Enter a title, save, and click the task title to open modal
3. Edit the task description
4. See "Edited by" section below the description

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.