Add sample using docker image with a mounted volume

We have some examples on how to use our server docker image in a few different ways, but it should also be possible to use a mounted volume to persist a local cluster between runs. (The current example loses all data after the cluster shuts down (the intended use case being for developers to use it for local testing).) If the docker compose network is set up with a mounted volume on the host, then it should work except that docker's mounted file system doesn't support direct I/O (alas), so the start up script would need to set the proper knob (which maybe is worth showing in and of itself).

Locate the existing server Docker image example, its Docker Compose network configuration, and the startup script mentioned in the issue. Check how the current example handles cluster data, then add a mounted-volume example that preserves a local cluster between runs and configures the startup behavior required for Docker-mounted storage.

Written by the indexing model from the issue text.