We were occasionally trying to compute schema 2 version 1 signatures on the *unicode* representation, which was failing the signature check. This PR adds a new wrapper type called `Bytes`, which all manifests must take in, and which handles the unicodes vs encoded utf-8 stuff in a central location. This PR also adds a test for the manifest that was breaking in production.
This change ensures that if a manifest list is requested with an accepts header for a *schema 2* manifest, the legacy manifest (if any) is returned as schema 2 if it was pushed as a schema 2 manifest (rather than being auto-converted to schema 1)
If a namespace is present in the whitelist, all calls are sent to the OCI model instead of the Pre OCI model
Note that this does increase overhead for registry calls (since we need to lookup the namespace for every single call), but it should only be temporary until we've migrated all users over to the OCI data model
