added findByUserNameAsync to the interface and service

src/Infrastructure/Identity/IdentityService.cs

@@ -21,6 +21,24 @@ public class IdentityService(
 
         return user?.UserName;
     }
+    
+    public async Task<UserModel?> GetUserByUserNameAsync(string userName)
+    {
+        var response = await userManager.FindByNameAsync(userName);
+        
+        if (response == null) return null;
+
+        var userModel = new UserModel()
+        {
+            Id = response.Id,
+            UserName = response.UserName,
+            FirstName = response.FirstName,
+            LastName = response.LastName,
+            Email = response.Email,
+        };
+
+        return userModel;
+    }
 
     public async Task<(Result Result, string UserId)> CreateUserAsync(string userName, string password)
     {