Track expansions of test report summary widget on MR page through usage ping

Problem

Customers can view the test summary report on the MR page but we don't know how often they actually interact with the widget. It is hard to measure if changes to the report result in more views and value for customers.

Proposal

Add a tracking event that fires when people expand the test summary merge request widget.

The counters to add to known_events.yml are:

• test_summary_widget_total - add the user_id to the counter when the user (regardless of plan type) opens the test summary widget on an MR.

Details for known_events.yml

name: i_testing_summary_widget_total
  category: testing
  redis_slot: testing
  aggregation: weekly

Metric name already added to event dictionary (internal link).

This will apply to both Self Managed and gitlab.com users for tracking on the dashboard below.

Redis HLL Counters docs

Success Criteria

Paid GMAU for Browser Performance testing, displays on the Testing Group Metrics Sisense dashboard.

Original Writeup / copy from usage ping issue

Summary

We don't have a way to check how many users are using the feature - JUnit XML test report

We should count the number of projects which uses this feature, periodically.

In other words,

select count(distinct project_id) from ci_job_artifacts where file_type = 4;

Reference: https://docs.gitlab.com/ee/ci/junit_test_reports.html#comment-4059531199