Make use case of availablePaymentGateways more explicit #1110
Description
I have across several discussions about availablePaymentGateways webhook, it seems it is not obvious that users can control the output of the query. Perhaps we could make it more explicit
https://docs.saleor.io/docs/3.x/developer/extending/webhooks/synchronous-events/payment#listing-all-available-payment-gateways