Expose the registry name mapping methods

[Wwwsylvia]

As users may still need to do the mapping from docker.io to https://index.docker.io/v1/ in their code when using Store.Get(), Store.Put() and Store.Delete(), we can consider expose the existing mapping methods for their convenience.

We may export the following methods and may rename them if needed:

• oras-credentials-go/registry.go

  Lines 82 to 90 in 97227b1

  	func mapStoreRegistryName(registry string) string {
  	// The Docker CLI expects that the 'docker.io' credential
  	// will be added under the key "https://index.docker.io/v1/"
  	// See: https://github.com/moby/moby/blob/v24.0.0-beta.2/registry/config.go#L25-L48
  	if registry == "docker.io" {
  	return "https://index.docker.io/v1/"
  	}
  	return registry
  	}

• oras-credentials-go/registry.go

  Lines 92 to 100 in 97227b1

  	func mapAuthenticationRegistryName(hostname string) string {
  	// It is expected that the traffic targetting "registry-1.docker.io"
  	// will be redirected to "https://index.docker.io/v1/"
  	// See: https://github.com/moby/moby/blob/v24.0.0-beta.2/registry/config.go#L25-L48
  	if hostname == "registry-1.docker.io" {
  	return "https://index.docker.io/v1/"
  	}
  	return hostname
  	}