Add sampling mode buttons for flamegraph in the performance bar

What does this MR do and why?

References: #30275 (closed)

Make it possible to select the sampling mode for flamegraphs with a button in the performance bar.

This change added the flamegraph button to the performance bar to make it easier to generate a flamegraph of the current URL. That flamegraph was always sampled in wall mode. This change gives the user the option to generate the flamegraph in either wall, cpu or object mode.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

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

1. Open the performance bar with p + b
2. Select one of the sampling modes in the performance bar

Testing

Docs: http://main-ee-71556.178.62.207.141.nip.io/ee/administration/monitoring/performance/performance_bar.html

App: https://gitlab-review-30275-perf-vv95lk.gitlab-review.app

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.

Related to #30275 (closed)