fix(notifications): notify actors after activities insert / update using model callback methods

--> Remove sql triggers because most shared hosting plans prevent using them

app/Models/NotificationModel.php

@@ -1,47 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-/**
- * @copyright  2021 Ad Aures
- * @license    https://www.gnu.org/licenses/agpl-3.0.en.html AGPL3
- * @link       https://castopod.org/
- */
-
-namespace App\Models;
-
-use App\Entities\Notification;
-use Michalsn\Uuid\UuidModel;
-
-class NotificationModel extends UuidModel
-{
-    /**
-     * @var string
-     */
-    protected $table = 'notifications';
-
-    /**
-     * @var string
-     */
-    protected $primaryKey = 'id';
-
-    /**
-     * @var string
-     */
-    protected $returnType = Notification::class;
-
-    /**
-     * @var bool
-     */
-    protected $useTimestamps = true;
-
-    /**
-     * @var string[]
-     */
-    protected $uuidFields = ['post_id', 'activity_id'];
-
-    /**
-     * @var string[]
-     */
-    protected $allowedFields = ['read_at'];
-}