Add topic on calling web APIs from Blazor

[danroth27]

• HttpClient
• JSON helpers
• Setting fetch arguments for the request (see Implement Request credentials  dotnet/blazor#399 (comment))
• Making cross origin request

[stimms]

This sounds interesting. Do we want to surface the fact that the HttpClient is not the actual HttpClient and is actually fetch or is the feeling that the abstraction is so good nobody needs to know?

[guardrex]

Issue moved to aspnet/Docs.