Add Docs For Blazor Server SignalR Usage

[TanayParikh]

https://aka.ms/blazor-server-using-fallback-long-polling will point to a new docs page which discusses common pitfalls and troubleshooting steps to ensure WebSockets are utilized (ie. enabled on IIS, enabled on azure portal, etc.). May just end up extending https://docs.microsoft.com/en-us/aspnet/core/blazor/host-and-deploy/server?view=aspnetcore-6.0#signalr-configuration.

Originally posted by @TanayParikh in #36764 (comment)