[TASK] add extension key to composer.json

composer.json

@@ -14,6 +14,11 @@
   "replace": {
     "sgalinski/sg_youtube": "self.version"
   },
+  "extra": {
+    "typo3/cms": {
+    "extension-key": "sg_youtube"
+    }
+  },
   "autoload": {
     "psr-4": {
       "SGalinski\\SgYoutube\\": "Classes/"