`crane` package is the highest level of abstraction that GGCR provides,
it's easy to use, however it doesn't give user much control.
This change moves `OCIRepository` controller logic to a lower-level
`remote` package and makes handling of references more explicit with
`name.Repository`, `name.Digest` and `name.Tag`.
It also simplifies options builder, as there is no need to have separate
sets of options for cosign and crane.
Signed-off-by: Ilya Dmitrichenko <errordeveloper@gmail.com>