[Proposal] Embed credentials helper to simplify push / pull process

[b4nst]

Currently in order to push / pull an image from Google Artifact Registry, we have to use GoogleCloudPlatform/docker-credential-gcr to generate the proper ~/.docker/config.json. It works but there's a simpler UX solution: using the helper directly.

It's done by Kaniko for example:

https://github.com/GoogleContainerTools/kaniko/blob/eea12bd0259c37f04443cca47f4aac3bf82d8c31/tools/tools.go#L25-L27