[Blazor] Guidance on limiting circuits per user

[javiercn]

We don't have any mechanism that out of the box limits the number of circuits a user/ip can create, but this is achievable through current extensibility.

We should provide a sample that showcases this.

This can be achieved by keeping track of the endpoints that create circuits (for example through a handler on OnCircuitOpened) and capturing information (like the user principal or the client ip address) and using that to limit the connections per server instance.

[chrdlx]

What about clients that share the same internet IP ? Which is the typical case for companies that use NAT to give inside users internet access.

[javiercn]

Covered as part of https://github.com/aspnet/AspNetCore.Docs/pull/13962/files