Remove the Line from the ConstituentVxF model that Ignores the vxfref Property
The _ConstituentVxF_ model class is currently ignoring the `vxfref` property from that class using the `JsonIgnoreProperties` property. The problem surges when one wants to retrieve/read that property from a _ConstituentVxF_ object, which in this case is needed for the feature [#31](https://labs.etsi.org/rep/osl/code/org.etsi.osl.tmf.api/-/issues/31).
The fix can be done by removing the `JsonIgnoreProperties` line.
issue