feat(docs): add Cartridge Controller paymaster information (#579)

A follow-up to #569

Noting that unliked other Paymaster integrations, the Controller
requires no additional code-level configuration and can be managed
entirely through the [Slot
CLI](https://docs.cartridge.gg/slot/paymaster).

Author: fracek

docs/pages/docs/paymaster-providers.mdx

@@ -30,4 +30,10 @@ import { avnuPaymasterProvider } from "@starknet-react/core";
 
 const apiKey = "your-api-key";
 const provider = avnuPaymasterProvider({ apiKey });
-```
+```
+
+### Cartridge Paymaster
+
+Cartridge Paymaster is natively supported in the [Controller](https://docs.cartridge.gg/controller/overview) and requires no additional configuration.
+Transactions that match a Paymaster policy (indicating a contract address and entrypoint) will automatically be subsidized.
+Paymaster policies and budgets can be [managed through the Slot CLI](https://docs.cartridge.gg/slot/paymaster).