Document usage of new formfield props as an example

### Is your feature request related to a problem? Please describe.

We've made some changes to how form-fields work by extracting a few properties to be computed in the form-field parent class. This may be worth documenting here as per https://github.com/bpmn-io/form-js/pull/808#discussion_r1395723959

### Describe the solution you'd like

- will add details later :)

Start by reviewing the form-js PR 808 discussion linked in the issue and the existing examples in this repository. Clarify which extracted form-field properties need coverage, then document their usage as an example and verify that the example reflects the current form-field behavior.

Written by the indexing model from the issue text.