Returns the canonical list of event types delivered to partner webhook
endpoints — every string is a resource.action pair (e.g. patient.created,
customer_invoice.paid, membership.updated). Use this list to type-check
incoming webhook payloads against the platform's current event registry.
Today there is no per-endpoint subscription filter — once a webhook endpoint
is registered (POST /partner/webhook_endpoints), it receives the full set
of events emitted for the partner's connected practices. Implementations
should ignore unknown event types; new resource/action pairs may be added
without a version bump.