[10.x] searchableSync / unsearchableSync

[gdebrauwer]

In my projects, I always configure Scout to queue the jobs that make model(s) searchable or unsearchable. This works perfectly, but sometimes you want to make a model instantly unsearchable.
For example, in a project, I show a list that is based on a Scout search result. Each item has a delete button. Deleting an item and refreshing the list will mean the refreshed list has a high change of still containing the deleted item if the job that makes the item unsearchable has not finished yet.

This PR adds methods to easily make model(s) synchronously searchable/unsearchable even if Scout config will queue those actions by default.

config()->set('scout.queue', true);

// This will be queued
$models->searchable();
$models->unsearchable();

// This will happen synchronously even if 'scout.queue' config variable is set to true
$models->searchableSync();
$models->unsearchableSync();

The 'Sync' suffix for the method names is inspired by the 'dispatchSync' method on jobs in Laravel.