Modify submission behavior of the New/Edit Release page

What does this MR do?

Modifies the form submission behavior of the New/Edit Release pages.

Current behavior	New behavior
Pressing ⌘/Ctrl+Enter submits the form even when the form contains validation errors	⌘/Ctrl+Enter only submits the form if there are no validation errors
The ⌘/Ctrl+Enter keyboard shortcut only works inside the Release notes markdown textarea	⌘/Ctrl+Enter works anywhere in the form
Pressing Enter while searching for a milestone submits the form	Pressing Enter inside the milestone selector component does not submit the form

Testing locally

There is a small bug in the quick_submit utility that may appear when testing locally: #235499 (closed)

This will be fixed once !39225 (merged) is merged.

Update: This issue has been fixed 👍

More information

The New Release page can be found by navigating to Project Overview > Releases > New Release.

Click here for a screenshot of the New Release page

This MR makes no visual changes to the page.

Related to #214244 (closed)