Use request attributes bag

It is better to fetch the step parameter from the request's attribute-bag instead of query directly. So it is more flexible to be used as Route-Parameter. f.e.:

```xml
<route id="example_route" pattern="/my-form/{step}">
        <default key="_controller">example_controller:my-method</default>
        <default key="step">1</default>
</route>
```