Feature Request: Allow `--empty-oci-base` with `crane mutate`

[nheimlich]

Description
Currently creating an image with an empty OCI base and setting labels requires two separate commands: crane append --oci-empty-base followed by crane mutate. This can be streamlined by allowing the --oci-empty-base flag to be used directly with crane mutate.

Current Workflow

1. crane append --oci-empty-base --new_layer image.tar --new_tag registry.example.com/<example>/<name>:<tag>
2. crane mutate registry.example.com/<example>/<name>:<tag> --label <key>=<value>....

Purposed Workflow

1. crane mutate --oci-empty-base --append image.tar registry.example.com/<example>/<name>:<tag> --label <key>=<value>....

I'm would like to contribute to this effort and have a working sample of crane mutate with the --oci-empty-base flag added.

Benefits

• reduced number of registry interactions
• reduced number of commands to produce an oci artifact

[nheimlich]

Pull Request: #2051

[nheimlich]

friendly ping :) @imjasonh @jonjohnsonjr