Spree::Admin::UserController is for super admin user only. Moving to a
reflex simplifies the code by getting rid of a new route and a new stimulus
controller
It shouldn't be possible for the update to fail, as we are not sending
any parameter. Any other failure should be handled by rails already, ie
missing csrf token.
Simply rendering the edit form on the posted path is problematic. For example if you refresh the path you get a 404.
But if there's errors, we want to render the form with unsaved values so you can see the errors and try again.
