Be able to deactivate `cucumber.undefined-step`

### 🤔 What's the problem you're trying to solve?

Undefined step is not compatible with [bdd_widget_test](https://pub.dev/packages/bdd_widget_test) in dart.

I only want the ability to format to avoid differences between developers.

### ✨ What's your proposed solution?

Can disable `cucumber.undefined-step`

### ⛏ Have you considered any alternatives or workarounds?

_No response_

### 📚 Any additional context?

_No response_

Start by locating where the extension implements the `cucumber.undefined-step` diagnostic and how its settings are registered. Check whether the formatter path is separate, then verify that users can disable this diagnostic while formatting still works for Dart projects using bdd_widget_test.

Written by the indexing model from the issue text.