Resolve "Support runtime Visual Review configuration"

What does this MR do?

This code:

• adds the ability to enter a merge request ID directly into the toolbar,
• adds the option to save the ID to localStorage (as with the token),
• adds a link to change the ID once entered
• adds some more explanatory errors for 401 & 404
• saves the comment to session storage if the user navigates away without posting it

As usual, it can be tested live at https://review-app-test.sarahghp.now.sh/ and posts to sarahghp/review-app-tester!1. Please post nice things, like poetry.

(You can now of course try to post to other MRs, but since they don't exist, you will just get an error.)

item	remembered?	item	remembered	on reload	mr change click	logout click	content saved
token	no	mr id	no	back to enter token	back to mr enter, token in state till logout or reload	back to enter token, id not remembered	on logout click, on mr click, on relaod
token	yes	mr id	no	back to enter id	back to enter id	back to enter token, id not remembered	on logout click, on mr click, on relaod
token	no	mr id	yes	back to enter token, then direct to comment	back to enter id, token still in state till logout or reload	back to enter token, id not remembered	on logout click, on mr click, on relaod
token	yes	mr id	yes	comment	back to enter id	back to enter token, id not remembered	on logout click, on mr click, on relaod

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Links

• Issue: #64190 (moved)