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

feat(emailer): add Postmark and Resend providers

backend/Modules/Memberships/Contracts/IMembershipCancellationProcessor.cs

@@ -0,0 +1,6 @@
+namespace Hutopy.Modules.Memberships.Contracts;
+
+public interface IMembershipCancellationProcessor
+{
+    Task<DateTimeOffset?> CancelAsync(string subscriptionId, CancellationToken ct = default);
+}

backend/Modules/Memberships/Contracts/IMembershipNotifier.cs

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+namespace Hutopy.Modules.Memberships.Contracts;
+
+public interface IMembershipNotifier
+{
+    Task NotifyCheckoutSessionCompleted(string stripeSessionId, string stripeSubscriptionId,
+        string userId,
+        string creatorId,
+        string tierId,
+        CancellationToken cancellationToken = default);
+
+    Task NotifyPaymentSucceedAsync(
+        string stripeSubscriptionId,
+        string hostedInvoiceUrl,
+        decimal amount,
+        string currency,
+        CancellationToken cancellationToken = default);
+
+    Task NotifySubscriptionUpdatedAsync(
+        string subscriptionId,
+        DateTimeOffset? endDate,
+        CancellationToken cancellationToken = default);
+
+    Task NotifySubscriptionDeletedAsync(
+        string subscriptionId,
+        CancellationToken cancellationToken = default);
+}

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);
+}

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);
+}

backend/Modules/Memberships/Contracts/MembershipCheckoutSession.cs

@@ -0,0 +1,6 @@
+namespace Hutopy.Modules.Memberships.Contracts;
+
+[PublicAPI]
+public record MembershipCheckoutSession(
+    string Id,
+    string Url);