Removes the `ENTRYPOINT` directive in the `contracts-bedrock` image. While convenient, using `ENTRYPOINT` makes building tooling on top of the image much harder since the entrypoint cannot be overridden without providing special flags to Docker. It is easier to use a dummy `CMD` instead that directs users to call specific tools when running the container. Functionally, this means users will run `docker run just <cmd>` instead of `docker run <cmd>` if they want to use the Justfile.