Add pure OCI Resolver

[jdolitsky]

Should create a Resolver that does not contain Docker-specific logic

For more info, please see opencontainers/tob#68 (comment)

[nishakm]

I'd like to help with this. Do we need to re-implement Resolver from scratch or is there an oci lib we can use?

[deitch]

I use google/go-containerregistry a lot.

[nishakm]

IIRC google's go-containerregistry also uses docker's Resolver.

[deitch]

I've spent so long in their code, I should know that. 😆

I'm away from laptop now, so cannot check.

[nishakm]

I'm certainly no expert! I can dig into the code some more. Still, I have recently tried to use go-containerregistry to pull an index.json with no luck.

[shizhMSFT]

@jdolitsky I lost context on this issue. Please re-open if it still need to be resolved. /cc @SteveLasker