extend the sniffing capability to head out to the endpoint

[pvgenuchten]

i hoped this service would run a ?service=wms/wcs/csw/wfs/wmts&request=getcapabilities against the endpoint, to evaluate if it returns a valid response.
Does it make sense to work on a PR to this lib which introduces that functionality, maybe with an extra param mode=extended?

I guess this would then include owslib to actually grab the capabilities?

A challenging aspect is that currently geolinks.sniff returns a single protocol, however endpoints often support mulitple protocols, so the expected output would be an array of supported protocols...