Configurable doctype for ValidityDateFilterPredicate

The doctype for ValidityDateFilterPredicate can be configured now via DoctypeConfigurationProperties.

(CMS-23232)

Expose linked settings in default schema

Add a new field "linkedSettings" to the default content schema to allow out of the box, easy access to linked settings. This feature is non breaking, since its just an addition to the content schema.

(CMS-18856)