Reimplement/define how to add datamodels to KB

[francescalb]

We have to decide and define how to put datamodels into the KB.
It should use the tableparsing for datamodels form dlite.

This is the old implementation that has been removed:

def save_extra_content(ts: Triplestore, source: dict) -> None:
    """Save extra content in `source` to the triplestore.

    Currently, this includes:
    - statements and mappings
    - data models (require that DLite is installed)

    Arguments:
        ts: Triplestore to load data from.
        source: Dict in multi-resource format.

    """
    import requests

    # Save statements and mappings
    statements = get_values(source, "statements")
    statements.extend(get_values(source, "mappings"))
    if statements:
        ts.add_triples(statements)

    # Save data models
    datamodels = {
        d["@id"]: d["datamodel"]
        for d in source.get("Dataset", ())
        if "datamodel" in d
    }
    try:
        # pylint: disable=import-outside-toplevel
        import dlite
        from dlite.dataset import add_dataset
    except ModuleNotFoundError:
        if datamodels:
            warnings.warn(
                "dlite is not installed - data models will not be added to "
                "the triplestore"
            )
    else:
        for url in get_values(source, "datamodelStorage"):
            dlite.storage_path.append(url)

        for iri, uri in datamodels.items():
            ok = False
            r = requests.get(uri, timeout=3)
            if r.ok:
                content = (
                    r.content.decode()
                    if isinstance(r.content, bytes)
                    else str(r.content)
                )
                dm = dlite.Instance.from_json(content)
                add_dataset(ts, dm)
                ok = True
            else:
                try:
                    dm = dlite.get_instance(uri)
                except (
                    dlite.DLiteMissingInstanceError  # pylint: disable=no-member
                ):
                    # __FIXME__: check session whether to warn or re-raise
                    warnings.warn(f"cannot load datamodel: {uri}")
                else:
                    add_dataset(ts, dm)
                    ok = True

            if ok:
                # Make our dataset an individual of the new dataset subclass
                # that we have created by serialising the datamodel
                ts.add((iri, RDF.type, uri))