ApiReview: IHttpClientCertificateFeature

[Tratcher]

Rename to ITlsConnectionFeature

What else should be added to this? The tls token binding?

[Tratcher]

Also fix the cert type: #279

[Tratcher]

There is already a ITlsTokenBindingFeature for token binding. It's a significantly different feature and it's OS specific, so lets not combine it with ITlsConnectionFeature.