Add a tools container for clients

[chuck-confluent]

I think the all-in-one should include a tools container for client code so that people can volume map their client code into the docker compose network and run it against CP. See for example this README. That README was written to fill a gap in cp all in one, but I think it makes sense to consolidate effort and focus onto cp all in one as the go-to place for freeform sandbox development.