remove duplication in attributes

[pvgenuchten]

mcf had some duplication in the attributes section, maybe it was kept at its old location for backwards compatibility?
suggestion to clean up the second instance

also a suggestion to extend sample with more relevant content
extend the field types with date and datetime

[pvgenuchten]

Some discussion about the expected values in the type property of attributes. From the json-schema perspective the typical json types would be expected (and date would be a formatter of string). However from a iso19110/iso19103 perspective typical valueTypes expected are:

suggestion could be to add a (optional) paremeter valueType (from Attribute.FC_FeatureAttribute.vaIueType)