Upgrade WebSocket live update to use WebSocketSubscription2021 where available

[timbl]

WebSocketSubscription2021 is a new more secure version of the web sockets protocol .

• Be back-compatible: use he old protocol where only it is available.

• Suggest implement a short-cut discovery by converting the Update-via: header discovery to work for WebSocketSubscription2021

Also do the loner discovery which is being developed. when that is available.

[timea-solid]

Looking at the new spec, webSockets need authentication which means - we need in rdflib authentication - or (rather how I'd do) pass to the UpdateManager the authSession (this might be enough). Remark: the place that needs change is: https://github.com/linkeddata/rdflib.js/blob/main/src/update-manager.ts#L616