feat: Created AdminAuthenticate middleware & register in Kernel

* If the user is not authenticated then redirects back to the admin login form. So we created  `AdminAuthenticate` middleware which helps to protect our dashboard

* We register this Middleware class `AdminAuthenticate` in Kernel with the short name `auth.admin` so we can consume this one easily on our routes.

app/Http/Kernel.php

@@ -54,6 +54,7 @@ class Kernel extends HttpKernel
      */
     protected $routeMiddleware = [
         'auth' => \App\Http\Middleware\Authenticate::class,
+        'auth.admin' => \App\Http\Middleware\AdminAuthenticate::class,
         'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,
         'cache.headers' => \Illuminate\Http\Middleware\SetCacheHeaders::class,
         'can' => \Illuminate\Auth\Middleware\Authorize::class,

app/Http/Middleware/AdminAuthenticate.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace App\Http\Middleware;
+
+use Illuminate\Auth\Middleware\Authenticate as Middleware;
+
+class AdminAuthenticate extends Middleware
+{
+    /**
+     * Get the path the admin should be redirected to when they are not authenticated.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @return string|null
+     */
+    protected function redirectTo($request)
+    {
+        if (! $request->expectsJson()) {
+            return route('admin.login');
+        }
+    }
+}