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

feat(emailer): add Postmark and Resend providers

backend/Infrastructure/Payments/Stripe/Services/MembershipCancellationProcessor.cs

@@ -0,0 +1,28 @@
+using Hutopy.Modules.Memberships.Contracts;
+using Stripe;
+
+namespace Hutopy.Infrastructure.Payments.Stripe.Services;
+
+public sealed class MembershipCancellationProcessor
+    : IMembershipCancellationProcessor
+{
+    public async Task<DateTimeOffset?> CancelAsync(
+        string subscriptionId,
+        CancellationToken ct = default)
+    {
+        SubscriptionService subscriptionService = new();
+
+        // Stripe - Cancel Subscription immediately
+        // var subscription = await subscriptionService.CancelAsync(
+        //     subscriptionId,
+        //     cancellationToken: ct);
+
+        // Stripe - Cancel Subscription AtPeriodEnd
+        Subscription? subscription = await subscriptionService.UpdateAsync(
+            subscriptionId,
+            new SubscriptionUpdateOptions { CancelAtPeriodEnd = true },
+            cancellationToken: ct);
+
+        return subscription.CancelAt ?? subscription.CanceledAt;
+    }
+}