Implement editing work item notes

What does this MR do and why?

This MR adds an ability to edit work item notes.

Screenshots or screen recordings

Updating a note

update_note_success

Cancel updating a note

update_note_cancel

Error updating a note

Known issue: our alert is not sticky so it's not obvious to the user what has happened when the note update fails

update_note_error

How to set up and validate locally

1. Enable the work items MVC feature flag

   Feature.enable(:work_items_mvc)

2. Open any work item
3. Add a few notes
4. Click on the pencil icon of the note
5. Change note text and click Save changes

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.

Related to #389968 (closed)