Add provenance pull flow for official images

Add support for pulling signed images from a version 2 registry.
Only official images within the library namespace will be pull from the
new registry and check the build signature.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
Push flow

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)