Move notes to work_items_mvc feature flag

What does this MR do and why?

Move the work item notes widget from work_item_mvc_2 to work_item_mvc feature flag

Screenshots or screen recordings

No UI changes

How to set up and validate locally

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

1. Enable the work_items_mvc flag

   Feature.enable(:work_items_mvc)

2. See that you can see the work item notes on any task

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.