Provide Microsoft.Extensions.Http.Polly package README

[MackinnonBuck]

Contributes to #48392

[halter73]

LGTM. @martincostello Do have any thoughts?

[martincostello]

Do have any thoughts?

The document looks fine to me as-is.

One thought I had thought I had though was maybe it would be worth a comment encouraging people to use to the new resilience libraries from dotnet/extensions that use the new Polly.Core APIs? There have been a few issues where people have asked when this package will be updated to use Polly v8 and I've had to explain the sort-of fork that's happened and that this package is kinda frozen and the new innovation is in the new extensions package.

[MackinnonBuck]

One thought I had thought I had though was maybe it would be worth a comment encouraging people to use to the new resilience libraries from dotnet/extensions that use the new Polly.Core APIs?

That's a good idea. I've updated the README to include such a note. Some of our docs even go as far as to say that Microsoft.Extensions.Http.Polly is deprecated, although the ASP.NET Core docs don't mention this, and we're still shipping new versions. Maybe we should consider not shipping new versions of this package (and updating the ASP.NET Core docs).

[martincostello]

Maybe we should consider not shipping new versions of this package (and updating the ASP.NET Core docs).

Maybe for .NET 10? It's a non-trivial piece of work to swap from one to the other, so at this stage it would be a bit of annoying rug-pull for users.