Allow ability to hook into users blueprint

[jelleroorda]

What is quite neat in my opinion is the following snippet from the Statamic\Http\Controllers\CP\Users\UsersController@edit (with also code going along in the update method of course):

$blueprint = $user->blueprint();

if (! User::current()->can('edit roles')) {
    $blueprint->ensureField('roles', ['read_only' => true]);
}

if (! User::current()->can('edit user groups')) {
    $blueprint->ensureField('groups', ['read_only' => true]);
}

Would it be possible to add an event to the edit and update method of the controller, so we can add extra fields that may be read-only for some users, and editable for others in the same way?

[jasonvarga]

Keep an eye on statamic/cms#2983