fix: annotate the catalogue data model with Health-RI DCAT standard

[YpeZ]

This PR attempts to annotate the data catalogue model with the semantics of Health-RI's Core Metadata Specification Schema.

In this branch I have opted for the Collections table to be referred to as a dct:DatasetSeries class.

[BrendaHijmans]

Are Studies/Cohorts Datasets or DatasetSeries? Instead use Distributions for Datasets table?

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud