Composer: allow plugins

The `dealerdirect/phpcodesniffer-composer-installer` Composer plugin is used to register external PHPCS standards with PHPCS.
The `composer/installers` Composer plugin is used to install the plugin in the correct directory in a WordPress context.

As of Composer 2.2.0, Composer plugins need to be explicitly allowed to run. This adds the necessary configuration for that.

Refs:
* https://blog.packagist.com/composer-2-2/#more-secure-plugin-execution

Author: jrfnl

composer.json

@@ -58,6 +58,10 @@
         ]
     },
     "config": {
-        "classmap-authoritative": true
+        "classmap-authoritative": true,
+        "allow-plugins": {
+            "dealerdirect/phpcodesniffer-composer-installer": true,
+            "composer/installers": true
+        }
     }
 }