Payin template ready

Webhook event triggered when a payin template finishes its payment-token setup and moves to ready.

From this point the template can accept payins. payment_tokens carries one entry per method that issues a token the payer addresses the payment to — for co_breb, the Bre-B key and its QR when one was requested. Methods that need no token (the payer is sent to the provider instead, as with co_pse) have no entry there.