[3.2-rc] Document Blazor `loadBootResource` configuration option

[captainsafia]

Recently, a loadBootResource option was added to Blazor's JS API (link) that allows users to configure where different app resources should be loaded from.

We should add some documentation (perhaps under the Host + Deploy) section that explains to users how this API can be used.

Blazor.start({
  loadBootResource: function (type, name, defaultUri, integrity) {
    if (type === "timezonedata") {
      return "https://my-awesome-cdn.com/" + name;    
    }
  },
});

Some scenarios that this API can be used for:

• Allow users to load static resources (like timezone data or dotnet.wasm) from CDN
• Loading compressed assemblies using a HTTP request and decompressing them on the client for hosts that don't support fetching compressed contents from the server
• Aliasing resources to a different name by redirecting each fetch request to the new name

cc: @javiercn @SteveSandersonMS