style(user_management): adjust created at column size

- Change ColumnSize.M to ColumnSize.S for the 'created at' column in the users page table

Author: fulleni

lib/user_management/view/users_page.dart

@@ -136,7 +136,7 @@ class _UsersPageState extends State<UsersPage> {
                     ),
                     DataColumn2(
                       label: Text(l10n.createdAt),
-                      size: ColumnSize.M,
+                      size: ColumnSize.S,
                     ),
                     DataColumn2(
                       label: Text(l10n.actions),