Display a message when updating a user from grid with duplicate email address

### What does it do ?

* reset the grid record on error (when trying to save/edit from a grid) and trigger the `afterAutoSave` event, even on failure
* add a notification of the error when editing a user in case of duplicated email.

### Why is it needed ?

When updating a record from a grid, there is no feedback when an error occurs (beside the record being marked as "dirty" (red triangle).

Since i did not check all processors to make sure they all return the error message the same, i only added a notification (`MODx.msg.alert`) for the users grid.

### Related issue(s)/PR(s)

* #11273