Add reminder notification for onboarding/offboarding helpers + admins

[WhiteHoodHacker]

If the helper role or admin role is added or removed to any member in the server, a notification ping should be sent in an admin-only channel with a reminder to reference the onboarding/offboarding guide in the central logistics document. This reminder is to ensure that permissions are synced across all external assets, including Trello, GitHub, and Google Drive.