Feature: The parameter podman_credential_files is used to provide containers-auth.json
files which allow authentication to registries. See README.md for more infomation.

Reason: Users need a way to provide credential files for authenticating to private
registries. Some operations may need to pull images from registries in an
automated or unattended way, and cannot use `registry_username` and `registry_password`.

Result: Users can provide registry credentials for automated and
unattended operations.