Add InitializePaymentRequestAsync method for stripe

[erincdustin]

This PR introduces a new method, InitializePaymentRequestAsync(), to the Catalyst Stripe integration. It's designed to support advanced Stripe payment flows (e.g, Stripe Elements or Payment Element) by returning a client_secret used to initialize the Stripe iframe on the frontend.

New Features
InitializePaymentRequestAsync()

• Accepts an AuthorizeCCTransaction request.
• Creates a PaymentIntent using Stripe’s API with AutomaticPaymentMethods.Enabled = true.
• Returns a CCTransactionResult with the Stripe client_secret populated in the TransactionID property.

Usage

• The TransactionID (which holds the client_secret) can be passed directly to the frontend and used to initialize Stripe Elements.
• Designed to work with frontend setups using stripe.confirmCardPayment().