Data list - Update expandable demo to match core

**Is this a new component or an extension of an existing one?**
Data list

**Describe the feature**
Update the [expandable data list demo](https://www.patternfly.org/v4/components/data-list/react-demos#expandable-control-in-toolbar) to be a full page demo that matches core implementation.

Core PR: https://github.com/patternfly/patternfly/pull/4784
