Add support for running against a local docker image.

[codebymikey]

When trying to test lando against a locally built image, it makes an attempt to call docker-compose pull to pull, but crashes because the docker image doesn't exist in an upstream repo.

We should probably be building with docker-compose build --pull instead rather than have it as two separate commands (it's probably more performant too).

---

Example .lando.yml file:

# file: .lando.yml
name: docker-test
services:
  test:
    type: compose
    app_mount: delegated
    overrides:
      # This image only exists locally for now, so Lando should be able to use it just fine.
      image: docker-test/only-locally-available
      command: tail -f /dev/null