[TASK] add extension key to composer.json

composer.json

@@ -17,6 +17,11 @@
   "replace": {
     "sgalinski/df_tabs": "self.version"
   },
+  "extra": {
+    "typo3/cms": {
+      "extension-key": "df_tabs"
+    }
+  },
   "autoload": {
     "psr-4": {
       "SGalinski\\DfTabs\\": "Classes/"