HttpClientFactory 2.1 feature

[glennc]

This is a tracking issue and description of the initial HTTPClientFactory implementation.

I will update this in the near future with the description of the overall direction for 2.1.

Issues will be tracked in this project: https://github.com/aspnet/HttpClientFactory/projects/1

In general the 2.1 milestones will be accurate for details of work being done.

[rynowak]

Closing this issue as done 👍

The only thing we wanted to do, but couldn't to get done is logging for Polly policies https://github.com/aspnet/HttpClientFactory/issues/86