HTTP/2 Negotiations prior knowledge #1547

Seems like today there is no way of controlling the http/2 negotiation, h2 has three options all supported by RFC https://python-hyper.org/projects/hyper-h2/en/latest/negotiating-http2.html ,It must be possible to pick which option to use especially the prior knowledge since right now this fails when attempting connection to http/2 server that doesn't negotiate.