registry: getting Endpoint ironned out

Signed-off-by: Vincent Batts <vbatts@redhat.com>
Update libtrust version

Updated to version of libtrust with the trust graph implementation

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