Returns an arbitrary value, representing a schema for the settings of
the FieldType.
Explanation: There are no possible generic schemas for defining settings
input, which is why no schema for the return value of this method is
defined. It is up to the implementer to define and document a schema for
the return value and document it. In addition, it is necessary that all
consumers of this interface (e.g. Public API, REST API, GUIs, ...)
provide plugin mechanisms to hook adapters for the specific FieldType
into. These adapters then need to be either shipped with the FieldType
or need to be implemented by a third party. If there is no adapter
available for a specific FieldType, it will not be usable with the
consumer.
