[bug] Support import of provisioners from _private_ OCI/image registry

[mathieu-benoit]

Now that we support the import of provisioners from public OCI registry/image with #48, let's now support the import of provisioners from private OCI registry/image.

High level flow to support this:

$ docker login|oras login...
$ ...--import oci.//...

Currently, the oci provisioner import does not inherit the docker creds or any other registry sessions, so private registries cannot be used.

Thoughts here but open to suggestion, we should just support the dynamic login approach ("using Docker credentials") like illustrated here: https://github.com/oras-project/oras-go/blob/main/example_test.go#L106, as opposed to support static approach like with user/passwork or token.

[7h3-3mp7y-m4n]

I like the dynamic login approach which is also mentioned here: https://github.com/oras-project/oras-go/blob/main/example_test.go#L121 , It can also improve the user experience :)
And I would love to work on it :)

[astromechza]

Yeah if it's easy enough and we already have the code in the oras library, then we should do this 👍

[astromechza]

done in #48 and #59