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

feat(emailer): add Postmark and Resend providers

backend/Modules/Memberships/Contracts/IMembershipTierProcessor.cs

@@ -0,0 +1,11 @@
+namespace Hutopy.Modules.Memberships.Contracts;
+
+public interface IMembershipTierProcessor
+{
+    Task<string> CreateAsync(
+        Guid creatorId,
+        Guid tierId,
+        string productName,
+        string currencyCode,
+        decimal amount);
+}