`conformance` relation type

[m-mohr]

Some OGC APIs use conformance and some use http://www.opengis.net/def/rel/ogc/1.0/conformance. Clarify which to use.

[m-mohr]

OGC API - Features and STAC API use conformance. We may need to switch to http://www.opengis.net/def/rel/ogc/1.0/conformance in the future as OGC API - Features may adopt it in subsequent versions and such STAC API may inherit it. Something potentially for openEO API v2.