Add identifying annotations to serialized JSON input to KeyWrap and KeyUnwrap

See: https://developer.ibm.com/articles/enabling-advanced-key-usage-and-management-in-encrypted-container-images/

Currently, we're only able to pass a simple string as an additional argument during encryption and decryption:

`OCICRYPT_KEYPROVIDER_CONFIG=ocicrypt.conf skopeo copy --multi-arch all --encryption-key provider:pilot:testkey oci:busybox oci:encrypted`

It would be better if we could include more identifying information in this string/annotation, possibly even a file, for example:

`OCICRYPT_KEYPROVIDER_CONFIG=ocicrypt.conf skopeo copy --multi-arch all --encryption-key provider:pilot:{"kms": "vault", "kek_id": "abc123"} oci:busybox oci:encrypted`

or

`OCICRYPT_KEYPROVIDER_CONFIG=ocicrypt.conf skopeo copy --multi-arch all --encryption-key provider:pilot:@key.json oci:busybox oci:encrypted`

key.json:
```json
{
"kms": "vault",
"kek_id": "abc123"
}
```