Rename `oci.manifest.digest` to `container.oci.manifest.digest` or similar

See https://github.com/open-telemetry/semantic-conventions/pull/1337#discussion_r1745833352 for the context.

OCI is ambiguous (Oracle Cloud Infrastructure and Open Container Initiative) and also is only widely recognized in the context of containers.

We should call it `container.oci.*`. 