Add human-only version of manage.events metric

What does this MR do and why?

Add human-only version of manage.events metric

This adds a new metric usage_activity_by_stage_monthly.manage.events_human_users that tracks distinct human users who generate manage events, excluding all bot types.

The original usage_activity_by_stage_monthly.manage.events metric includes both human users and bots (project_bot, alert_bot, support_bot, etc.) which can inflate UMAU counts. This new metric provides an accurate count of only human users for better customer health scoring.

Bot types excluded: project_bot (used by project and group access tokens), alert_bot, support_bot, visual_review_bot, migration_bot, security_bot, automation_bot, security_policy_bot, admin_bot, service_account, duo_code_review_bot

Changelog: added

References

Contributes to #548411

How to set up and validate locally

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