Returned `rel` link for tiling scheme is wrong

[francbartoli]

While I was trying to check the OpenLayers demo https://openlayers.org/en/latest/examples/ogc-vector-tiles.html out with an online TiPG deployment https://jcaujxxvec.execute-api.eu-west-1.amazonaws.com/api/docs I realize the following:

• Using https://jcaujxxvec.execute-api.eu-west-1.amazonaws.com/api/collections/adam.adam_ts_tracks/tiles/WebMercatorQuad as the url value for the OGCVectorTile the demo doesn't work as expected
• After a bit of debugging on the client code I have figured out that this exception is raised

  throw new Error(
     "Expected http://www.opengis.net/def/rel/ogc/1.0/tiling-scheme link or tileMatrixSet"
   );

• After a further analysis on the payloads returned by TiPG I have found that the endpoints with the tiling scheme return a rel link with the plural form of the IRI tiling scheme http://www.opengis.net/def/rel/ogc/1.0/tiling-schemes while OL expects clearly the singular form http://www.opengis.net/def/rel/ogc/1.0/tiling-scheme according to https://docs.ogc.org/is/20-057/20-057.html#toc30 section 8.2.2 Requirement 8 Identifier D and confirmed by the exception