annotations aren't added if --provenance=false

[apetrosyan1613]

Hi there! I've spent some time to find the reason for missing annotations within docker buildx imagetools create command.

The reason is here

When the --provenance flag is set to true, we have two different media types:
Expected: application/vnd.oci.image.index.v1+json
Actual: application/vnd.docker.distribution.manifest.list.v2+json

So, what do we have: annotations for multi-arch builds are added only if we have enabled the provenance flag

I'm not sure if it's a bug, but I'll be glad if anyone can explain to me, why this behavior is expected.

Thanks!