Allow adding requests to performance bar manually

What does this MR do?

Add a '+' button in the performance bar. When clicked, it allows you to enter a request ID or a URL. A request ID will fetch performance bar results for that request, and a URL will fetch that URL and then its performance bar data.

Because of the way it's triggered, the URL will use the current user's credentials, and it must be to a JSON endpoint - that's the content type it will request. A request ID can be for any request (HTML, JSON, XML, images) and can be for any user.

For #28636 (closed).

Screenshots

Add a JSON request by URL:

Add any request by ID:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created

Performance and Testing

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