Recreate Redis Counters using Snowplow events - Phase 2: Wave 5b -BE EVENTS

Summary

In &7493 (closed), we instrumented the first set of Redis Counters using Snowplow events in SaaS. This is the 5th wave of counters to be instrumented using Snowplow Events. Splitting this counter, redis_hll_counters.epics_usage.epics_usage_total_unique_counts_monthly, into its own issue per this comment since the counter is made up of many sub-metrics.

1. redis_hll_counters.epics_usage.epics_usage_total_unique_counts_monthly => THIS COUNTER WILL BE COMPLETE WITH THE CLOSURE OF #370373 (closed)

Submetrics that need to be migrated:

1. g_project_management_epic_created
2. project_management_users_unchecking_epic_task
3. project_management_users_checking_epic_task
4. g_project_management_users_updating_epic_titles
5. g_project_management_users_updating_epic_descriptions
6. g_project_management_users_creating_epic_notes
7. g_project_management_users_updating_epic_notes
8. g_project_management_users_destroying_epic_notes
9. g_project_management_users_awarding_epic_emoji
10. g_project_management_users_removing_epic_emoji
11. g_project_management_users_setting_epic_start_date_as_fixed
12. g_project_management_users_updating_fixed_epic_start_date
13. g_project_management_users_setting_epic_start_date_as_inherited
14. g_project_management_users_setting_epic_due_date_as_fixed
15. g_project_management_users_updating_fixed_epic_due_date
16. g_project_management_users_setting_epic_due_date_as_inherited
17. g_project_management_epic_issue_added
18. g_project_management_epic_issue_removed
19. g_project_management_epic_issue_moved_from_project
20. g_project_management_users_updating_epic_parent
21. g_project_management_epic_closed
22. g_project_management_epic_reopened
23. 'g_project_management_issue_promoted_to_epic'
24. g_project_management_users_setting_epic_confidential
25. g_project_management_users_setting_epic_visible
26. g_project_management_epic_users_changing_labels
27. g_project_management_epic_destroyed
28. g_project_management_epic_cross_referenced
29. g_project_management_users_epic_issue_added_from_epic [FRONTEND EVENT] Addressed in #370373 (closed)
30. g_project_management_epic_related_added
31. g_project_management_epic_related_removed
32. g_project_management_epic_blocking_added
33. g_project_management_epic_blocking_removed
34. g_project_management_epic_blocked_added
35. g_project_management_epic_blocked_removed

Feature Flag

These events should be instrumented behind a feature flag (separate from the FF used for the first wave of metrics) in case we need to quickly turn off collection.

Next Step

Post delivery, the data team will need to aggregate the snowplow events into counters for use in Sisense and Gainsight. Data team issue for this wave: https://gitlab.com/gitlab-data/analytics/-/issues/13211