Sylius refund plugin support

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Sylius Refund Plugin Integration

This branch adds full integration with Sylius Refund Plugin for both Stripe Checkout and Stripe Web Elements payment methods.

Features

• Automatic Stripe Refund Processing: When a refund is generated through Sylius Refund Plugin, the plugin automatically creates and dispatches a payment request to process the refund via Stripe API.
• Partial Refund Support: Full support for partial refunds, allowing administrators to refund specific amounts rather than the full payment.
• Gateway Auto-Registration: Stripe gateways are automatically added to the Sylius Refund Plugin's supported gateways list via a compiler pass.

Implementation Details

1. RefundPaymentGeneratedEventListener: Listens to RefundPaymentGenerated events and creates corresponding payment requests for Stripe refunds.

2. SyliusRefundSupportedGatewaysCompilerPass: Automatically registers Stripe payment factories as supported gateways in Sylius Refund Plugin.

3. Conditional Configuration: The integration is only loaded when Sylius Refund Plugin is installed, ensuring backward compatibility.

Testing

• Unit tests for RefundPaymentGeneratedEventListener and SyliusRefundSupportedGatewaysCompilerPass
• Behat scenarios for full and partial order refunds (Stripe Checkout and Web Elements)