Add support for retrying basic auth if bearer fails

[TerryHowe]

Add support for retrying basic auth if bearer fails

Similar to helm/helm#31212

[FeynmanZhou]

Introducing the auth fallback mechanism in the library makes sense to me as it makes the client authentication work with different registries. @oras-project/oras-go-maintainers any thoughts?

[Wwwsylvia]

SGTM, this aligns with the conclusion in #972 .