Implement DownloadTimeout and Retry

[pawelvds]

No description provided.

[volllly]

I would love if we could refactor the creation of the policies here into a helper class.

https://github.com/fiskaltrust/middleware-launcher/pull/91/files#diff-5479e5559a7e6c816be57a02b080271ac8cabcefe6f9128bfcb51df9f92ee7a4R26-R32

https://github.com/fiskaltrust/middleware-launcher/pull/91/files#diff-0080b553315406d4c6b2c9e39533463df4ba95c04b740c6e7539397ea2b2fa8fR26-R32

something like this
src/fiskaltrust.Launcher/Helpers/PolicyHelper.cs

static class PolicyHelper {
  public static IAsyncPolicy<HttpResponseMessage> CreateHttpClientPolicy(Launcher
configuration configuration) {
    // create policy here
  }
}

and then in the dowloaders just do this _policy = PolicyHelper.CreateHttpClientPolicy(configuration);