Stop audit events being deleted: everything, or named workspaces or people.

Organization admins only (403 organization_admin_required), on a browser session with a fresh proof in the x-50h-reauth header (401 reauth_required). It needs a person: API keys, connected apps and service accounts get 403 session_required. Every change is written to the organization's audit. Up to 50 open holds (409 too_many_holds). A workspace must be one of the organization's (404 workspace_not_found).