Add explicit BrowserRefresh logging filter

Added 'Microsoft.AspNetCore.Watch.BrowserRefresh' to Warning level
to suppress the 'Middleware loaded' and 'Script injected' debug messages
that appear when running with dotnet watch or Ctrl+F5 from Visual Studio.

src/ElectronNET.Samples.BlazorSignalR/appsettings.Development.json

@@ -6,6 +6,7 @@
       "Microsoft.AspNetCore.SignalR": "Warning",
       "Microsoft.AspNetCore.Http.Connections": "Warning",
       "Microsoft.AspNetCore.Watch": "Warning",
+      "Microsoft.AspNetCore.Watch.BrowserRefresh": "Warning",
       "Microsoft.Hosting.Lifetime": "Information"
     }
   }