Improve import and export VFC TOSCA attributes

Improve import and export VFC TOSCA attributes

Improve the import and export VFC TOSCA attributes, addressing the
following concerns:
- brings the import and export logic very close to the properties logic,
as they are very similar structures
- fix import/export default values for complex types and list of simple
or complex types
- fix export of unnecessary/empty attribute entries
- creation of attributes during the initialization (base types)
- inheritance of parent attributes

Change-Id: Ic733e3455fc256595b5c2b1f48e19a13be27b5cc
Issue-ID: SDC-3466
Signed-off-by: andre.schmid <andre.schmid@est.tech>