Refactor user registration process to use UserRegistrationDto;

implement user registration in seed app

web/backend/Features/Features.Auth/Dtos/UserRegistrationDto.cs

@@ -0,0 +1,10 @@
+namespace Features.Auth.Dtos;
+
+public record UserRegistrationDto(
+    string Username,
+    string FirstName,
+    string LastName,
+    string Email,
+    DateTime DateOfBirth,
+    string PasswordHash
+);