Convert g_project_management_users_epic_issue_added_from_epic to Internal Events

Problem

g_project_management_users_epic_issue_added_from_epic is part of epics_usage_total_unique_counts_monthly which we want to overall convert to internal events (see #421593 (closed)) It is separated out since it's a frontend event

Desired outcome

g_project_management_users_epic_issue_added_from_epic is converted to internal events and all metrics relying on it

Potential solution

TBD