Add additional links to generated STAC Items

[fmigneault]

Following are some Link Relations that should be considered for addition. They are considered "best practices" within STAC.

• via or convertedfrom: Identifies a resource that is the source of the information in the link's context.

  This should be used to reference to the original NcML, NetCDF, CORDEX, etc. external reference metadata that was employed to obtain the "derived" STAC metadata. Similar to the derived_from link, but more explicit about being the source of origin, though transformed.

• original or canonical: Represent the original "STAC" source.

  This could be relevant for example in the case of the directory loader.
  For instance, if a server offers both ${HOST}/data/{collectionID}/{itemID}.geojson and ${FQDN}/data/{collectionID}/{itemID}/{assetID}.{ext} as direct access to the files, the populated STAC API ${HOST}/stac/collections/{collectionID}/{itemID} endpoint could indicate canonical toward the reference ${HOST}/data/... location.

• 3d-tiles, wms, wmts, pmtiles, xyz, tilejson links if the corresponding service applies
  as per https://github.com/stac-extensions/web-map-links