This patch introduces hidden commands to control container
lifecycle:
- `npx playwright docker install-server-deps` to install fluxbox,
vnc, novnc & to configure them.
- `npx playwright docker run-server` to run a server inside the
container.
Drive-by: remove old version of container image when building a new
version with the same name. This way we won't pile up untagged
container images.
