Default query HTTP Idle timeout to 4.5s

HTTP Idle Timeout is not supported by HttpClientHandler which we are currently using, but (although not in .NET Standard yet) SocketsHttpHandler does support it:

https://docs.microsoft.com/en-us/dotnet/api/system.net.http.socketshttphandler.pooledconnectionidletimeout?view=netcore-3.1#System_Net_Http_SocketsHttpHandler_PooledConnectionIdleTimeout

"However, we're using HttpClientHandler, not SocketsHttpHandler:"

internal class AuthenticatingHttpClientHandler : HttpClientHandler

Possible solution: "maybe we need to make AuthenticatingHttpClientHandler descend from DelegatingHandler and then inject the base handler"