update horizon API docs to include SAC transfer type as an option for payment schemas

[mollykarcher]

What problem does your feature solve?

Docs for the /payments endpoint displays a toggle that lists all the possible operation types that the payment endpoint could return (https://developers.stellar.org/docs/data/horizon/api-reference/list-all-payments). However, the schema for when a payment is an SAC transfer is not there.

What would you like to see?

Update the docs to include the payment schema for an InvokeHostFunction