feat: support adding auth config to docker through DOCKER_AUTH_CONFIG

First of all, I'm not totally sure if this would completely fit in here. But I believe this could be a nice addition to the AWS support that currently gitlab has. I'm happy to try implement this somewhere else or to workaround it in a different way.

This is one of the options provided by the official documentation: https://docs.gitlab.com/ee/ci/docker/authenticate_registry.html#option-3-use-docker_auth_config And makes it possible to support more registry schemes.

This has been developed while following https://docs.gitlab.com/ee/ci/cloud_deployment/#deploy-your-application-to-ecs and having a private ECR registry. In this case, it becomes much easier to push to ECR instead to the gitlab registry, since it avoids a two-way authentication (where gitlab authenticates to AWS, and AWS authenticates to gitlab). For that same reason, also install the ecr-login docker credential.