Make writing relation count properties optional (#969)

* Make writing relation count properties optional

* Clean up description

* Add test for write_model_magic_where=false

* Add test for write_model_relation_count_properties=false

tests/Console/ModelsCommand/MagicWhere/Models/Post.php

@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+namespace Barryvdh\LaravelIdeHelper\Tests\Console\ModelsCommand\MagicWhere\Models;
+
+use Illuminate\Database\Eloquent\Model;
+
+class Post extends Model
+{
+}