Moves the ChangeUserAdminStatusRequest to the ApiModels folder.
Updates the admin controller route to "admin" and the admin status
endpoint to "adminStatus".
Makes the ChangeUserAdminStatus method asynchronous.
Uses NotFoundException instead of KeyNotFoundException.
Adds functionality to allow administrators to modify the admin status of other users.
Introduces an endpoint for changing user admin status, accessible only to existing administrators.
This change includes necessary services and request models to handle the logic.
