Initialize container volumes with local files

Context

Oftentimes, container deployments might need to be initialized with a certain set of local files.

Common examples include application-specific configuration files.

Currently, providing these files (especially in a freshly initialized project) is cumbersome, and consists of the following steps:

1. Provide an empty dummy app or container (e.g. static file app, or a busybox container)
2. Connect to that app, synchronize files (rsync or scp) into the project's /files directory or into a volume
3. Then mount that directory into the actual container.
4. Remove the temporary dummy app/container

Proposal

Imperative workflow (using container run)

Proposal: Add an additional volume mirror command that initializes a new volume that is automatically initialized from a local directory (alternatively, add a --initialize-from flag to the volume create command:

# alternative #1
user@local $ mw volume create config
user@local $ mw volume mirror ./config config

# alternative #2
user@local $ mw volume create --initialize-from=./config config

# usage
user@local $ mw container run -v config:/etc/config [...]

Declarative workflow (using stack deploy)

Proposal: Use docker-compose syntax (combined with a custom driver) to configure volume initialization:

volumes:
  config:
    driver: local-sync
    driver_opts:
      source: ./config

Start by reviewing the existing volume create, volume mirror, and stack deploy command entry points. Compare the two proposed workflows and define the supported initialization behavior and completion checks before implementation; the issue does not name files or tests.