Currently image references end up being stored in a
random order due to the way maps are iterated through
in Go. This leads to inconsistent identifiers being
resolved when a single reference is needed to identify
an image and the ordering of the references is used for
the selection.
Sort references in a consistent and ranked manner,
from higher information formats to lower.
Note: A `name + tag` reference is considered higher
information than a `name + digest` reference since a
registry may be used to resolve the digest from a
`name + tag` reference.
Signed-off-by: Derek McGowan <derek@mcg.dev>
