Create Dart snippets and reference them

Co-Authored-By: ok300 <106775972+ok300@users.noreply.github.com>

snippets/dart_snippets/lib/send_spontaneous_payment.dart

@@ -0,0 +1,15 @@
+import 'package:breez_sdk/breez_sdk.dart';
+import 'package:breez_sdk/bridge_generated.dart';
+
+Future<SendPaymentResponse> sendSpontaneousPayment({
+  required String nodeId,
+}) async {
+  // ANCHOR: send-spontaneous-payment
+  SendSpontaneousPaymentRequest req = SendSpontaneousPaymentRequest(
+    amountMsat: 3000000,
+    nodeId: nodeId,
+  );
+  SendPaymentResponse resp = await BreezSDK().sendSpontaneousPayment(req: req);
+  // ANCHOR_END: send-spontaneous-payment
+  return resp;
+}