Add ESLint rules for classic decorator

This is a part of the installation that I missed 😞

Author: backspace

ui/.eslintrc.js

@@ -33,6 +33,8 @@ module.exports = {
         checkLoops: false,
       },
     ],
+    'ember/classic-decorator-hooks': 'error',
+    'ember/classic-decorator-no-classic-methods': 'error',
   },
   overrides: [
     // node files