Support SignalR scenarios with Blazor Server

[mkArtakMSFT]

For example, how to do pub/sub from a Blazor Server apps.

Be able to host a new hub on the server and simulate loopback connections between the hubs or provide some other mechanism to subscribe to SignalR invocations on the server efficiently.

[nwoolls]

If this is a new effort it would be nice if this method worked with Blazor auto render mode as well, so that the same code / experience can start with Blazor Server and then move to Blazor WASM once assets have been downloaded.