[HVD] Dataset.distribution: The cardinality should be 0..*

[jimjyang]

[This was already raised in #376 when it was v.2.2. I couldn't see that this is solved now in v.3.0.0-hvd, so I raise it again]

The cardinality for the property Dataset.distribution (dcat:distribution) (dcat:distribution) is 1..*, while in the Annex A this property is catetorized as Recommended (thus 0..). So, it is at least inconsistency between the specification of the property and the quick reference in Annex A.

Furthermore, since Bulk Download in HVDR is mapped onto dcat:Distribution, and HVDR does not always require Bulk Download (e.g. "for historical versions of datasets: APIs or bulk download", conf. the last bullet point under 2.2.a in the HVDR Annex), the cardinality for this property should not be 1...

[Yes, it is of course possible to relate to a dcat:DataService indirectly via a dcat:Distribution in order to be compliant with the cardinality requirement 1..*, but no, this is not the way that 10.8 recommends]