List webhook subscriptions

Webhook subscriptions deliver patient.created, appointment.created, invoice.created and payment.created events (and their .updated / .deleted variants) to your server as signed POST requests (X-Doctofam-Signature: t=<timestamp>,v1=<hex HMAC-SHA256 of "timestamp.body">). An endpoint failing 20 times in a row is disabled automatically. Subscriptions are managed with an operator access token; the secret is only returned once, on create.