Support committing of Webform through SDK

[MBueschelberger]

At the moment, we are not able to commit the webform Field of the KTypes.

This has the reason that the webform is parsed during retrieval and turned into a pydantic model without inheriting the original webform fields.

This pydantic model from the webform then is passed to the related KItem the KType is instanciated for in order to build the custom_properties.

Ideally, this custom_properties model still should hold the original webform so that it can be serialized back to a json when commited.

Hence, the webform Field should be defined through a Pydantic model as well.

[MBueschelberger]

This has been addressed in v3.0.0. The logic with the custom properties and webform has been changed there.