docker2aci (library and standalone binary), should allow the callers to specify a union-set of acceptable registry and mediatype options. This is needed to let consumers specify a certain mediatype to avoid (eg. OCI before stabilization) or certain registry features to enforce (eg. downgrade to registry-v1 or enforce DCT).

From the CLI, this may translate into:

• --registry-options=[registry-v1,registry-v2,registry-v2-dtc] with an auto default covering plain v1+v2 for the moment.
• --mediatype-options=[docker-v1,docker-v2.1,docker-v2.2,oci-v1.pre] with an auto default covering docker types for the moment.

For the lib, this will translate into appropriate parameters to all backend types.