WebSocket server support

[pi0]

(there is an open discussion in winterCG but I suppose it is about client/connector: wintercg/proposal-common-minimum-api#66)

WebSocket server support is supported in various runtimes (Bun, Cloudflare, Deno, Node.js, uWS) and I'm not aware of any specific standard that even tries to unify them.

It is not an API so not sure if we like to include the test to the list, it would be mainly a manual, exotic flag, still I was still thinking it might be to mentioned if we like to include non-api features, but common enough ones to the list. Happy to close if there is no enough reasons to list it.