Add retries to performance_bar_spec E2E test assertion methods

What does this MR do?

Adds retries to has_detailed_metrics? and has_request_for? performance bar page object methods. This spec was failing because it wasn't finding text in the performance bar, even though screenshots show the text is present. Performing this test manually shows there is a lag between when the rest of the page renders and when the performance bar text renders.

This MR also adds a qa selector to the request dropdown element, and adds a step to expand the dropdown before searching for a specific request.

This MR does not de-quarantine the test. A separate MR will remove the :quarantine flag after we confirm the test is stable.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines