Docker image containing rust, rust nightly and some preinstalled packages used in CI

This image is manually maintained:

CLI

1. Edit
   1. ci/rust-version.sh for rust and rust nightly version
   2. ci/docker/Dockerfile for other packages
2. Ensure you're a member of the Solana Docker Hub Organization and already docker login
3. Run ci/docker/build.sh to build/publish the new image