feat: return organisationId if user is an organization

this will help to determine if an event is created by the user or not

WebApp/Mapping/UserMapping.cs

@@ -16,5 +16,18 @@ namespace WebApp.Mapping
                 user.IsOrganisation
             );
         }
+
+        public static UserSummaryWithOrgIdDto ToUserSummaryWithOrgIdDto(this User user, int OrganisationId)
+        {
+            return new UserSummaryWithOrgIdDto(
+                user.UserId,
+                user.Email,
+                user.FirstName,
+                user.LastName,
+                user.CreatedAt,
+                user.IsOrganisation,
+                OrganisationId
+            );
+        }
     }
 }