Support artifact policies in the registry

[toddysm]

With OCI registries becoming more versatile to host all kind of artifacts, customers want to restrict the ability to push any artifact type to the registry. For example, some customers want to enable only Bicep modules to be pushed and served from the registry. Other customers want to enforce locking for all artifacts pushed to the registry. The first step to get this enabled is to provide a way for ACR to support policies on the data plane.