Add config entries to ymls

Add event to known_events
Add default-true feature flag
Add changelog entry

config/feature_flags/development/usage_data_i_testing_load_performance_widget_total.yml

+---
+name: usage_data_i_testing_load_performance_widget_total
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/52688
+rollout_issue_url:
+milestone: '13.9'
+type: development
+group: group::testing
+default_enabled: true

ee/changelogs/unreleased/10687-track-load-performance-widget-expansions.yml

+---
+title: Track load performance widget expansions via usage ping
+merge_request: 52688
+author:
+type: added

lib/gitlab/usage_data_counters/known_events/common.yml

@@ -273,6 +273,11 @@
   redis_slot: testing
   aggregation: weekly
   feature_flag: usage_data_i_testing_group_code_coverage_project_click_total
+- name: i_testing_load_performance_widget_total
+  category: testing
+  redis_slot: testing
+  aggregation: weekly
+  feature_flag: usage_data_i_testing_load_performance_widget_total
 # Project Management group
 - name: g_project_management_issue_title_changed
   category: issues_edit