Merge pull request #658 from pantheon-systems/cms-471-allow-plugins

[CMS-471] Add allow-plugins config.

Author: kporras07

composer.json

@@ -44,6 +44,11 @@
     "sort-packages": true,
     "platform": {
       "php": "7.3"
+    },
+    "allow-plugins": {
+      "composer/installers": true,
+      "dealerdirect/phpcodesniffer-composer-installer": true,
+      "johnpbloch/wordpress-core-installer": true
     }
   },
   "extra": {