fix: Revert Helm v3 to OAuth2 workflow for OCI

ORAS v1 used POST for auth as part of OAuth workflow
ORAS v2 changed to GET for this
We can use the ForceAttemptOAuth2 setting to revert to prior behavior

This was not well-documented in the docker implementation used by ORAS 1

This is well-documented in the ORAS 2 OCI auth implementation:
https://github.com/opencontainers/wg-auth/blob/main/docs/implementations/ORAS.md?plain=1

Signed-off-by: Scott Rigby <scott@r6by.com>

pkg/registry/client.go

@@ -156,6 +156,8 @@ func NewClient(options ...ClientOption) (*Client, error) {
 			authorizer.Cache = auth.NewCache()
 		}
 
+		authorizer.ForceAttemptOAuth2 = true
+
 		client.authorizer = &authorizer
 	}