Update authentication with docker cli

[rgaiacs]

As reported in jupyterhub/mybinder.org-deploy#3253, BinderHub instances using Docker Hub as container registry will encounter authentication issues because base64 user:password and user:token is not accepted by Docker Hub.

We need to use

cat ~/my_password.txt | docker login --username foo --password-stdin

This is how the Docker's login GitHub Action operates, see https://github.com/docker/login-action/blob/327cd5a69de6c009b9ce71bce8395f28e651bf99/src/docker.ts#L35.

This change is limited to Docker Hub. For example, Project Quay continues to mention base64 user:token in their documentation.