feat: mock plugins with real configs

so you no longer need to comment out xpack config in the kibana.dev.yml

plugins/ml/index.js

@@ -0,0 +1,12 @@
+export function ml(kibana) {
+  return new kibana.Plugin({
+    name: 'ml',
+    id: 'ml',
+    configPrefix: 'xpack.ml',
+    config(Joi) {
+      return Joi.object({
+        enabled: Joi.boolean().default(true),
+      }).default();
+    },
+  });
+}