"Advanced" Section for HttpClientFactory Docs

There is a recent discussion on an issue in the [HttpClientFactory repo](https://github.com/aspnet/HttpClientFactory/issues/200#issuecomment-436791061) where @reisenberger highlighted a good use case for one of the less common overloads of the HttpClientBuilder.AddPolicyHandler method.

Would it be reasonable to consider adding a subpage under the [existing documentation](https://docs.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-2.1) which provides some real-world demonstration of when and how one might use some of these overloads and more advanced possibilities? Similar to the plans for the [Dependency Injection section](https://github.com/aspnet/Docs/issues/6312).

cc @glennc, @scottaddie and @rynowak