Notifications: Started back-end for watch system

Added DB and started controller method.

database/migrations/2023_07_31_104430_create_watches_table.php

@@ -0,0 +1,37 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::create('watches', function (Blueprint $table) {
+            $table->increments('id');
+            $table->integer('user_id')->index();
+            $table->integer('watchable_id');
+            $table->string('watchable_type', 100);
+            $table->tinyInteger('level', false, true)->index();
+            $table->timestamps();
+
+            $table->index(['watchable_id', 'watchable_type'], 'watchable_index');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        Schema::dropIfExists('watches');
+    }
+};