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

feat(emailer): add Postmark and Resend providers

backend/Modules/Identity/Contracts/KnownRoles.cs

@@ -0,0 +1,7 @@
+namespace Hutopy.Modules.Identity.Contracts;
+
+public static class KnownRoles
+{
+    public const string Administrator = nameof(Administrator);
+    public const string Creator = nameof(Creator);
+}