chore: add npm config to definitions

lib/config/definitions.js

@@ -565,6 +565,14 @@ const options = [
     description: 'Requested reviewers for Pull Requests (GitHub only)',
     type: 'list',
   },
+  {
+    name: 'npm',
+    description: 'Configuration object for npm package.json renovation',
+    stage: 'repository',
+    type: 'json',
+    default: {},
+    mergeable: true,
+  },
   {
     name: 'meteor',
     description: 'Configuration object for meteor package.js renovation',