CORS for api (#7292)

* Added CORS support to API

* Changed order so CORS will still work if throttle hit

* Added APP_CORS_ALLOWED_ORIGINS env option

* Fixed typo

* Clarified header comments

* More clarification

* DIsable CORS allowed origins by default to replicate existing behavior

* Change variable name to be clearer

app/Http/Kernel.php

@@ -44,6 +44,7 @@ class Kernel extends HttpKernel
         ],
 
         'api' => [
+            \Barryvdh\Cors\HandleCors::class,
             'throttle:120,1',
             'auth:api',
         ],