many fixes and improvements - rework for modules/ and common/

feat(emailer): add Postmark and Resend providers

backend/Modules/Memberships/Contracts/IMembershipPaymentProcessor.cs

@@ -0,0 +1,14 @@
+using Hutopy.Modules.Creators.Contracts;
+
+namespace Hutopy.Modules.Memberships.Contracts;
+
+public interface IMembershipPaymentProcessor
+{
+    Task<MembershipCheckoutSession> CreateCheckoutSessionAsync(
+        Guid userId,
+        CreatorReference creatorReference,
+        Guid tierId,
+        string priceId,
+        string successUrl,
+        string cancelUrl);
+}