* solana/devnet_setup.sh: Build CLI instead of JITing it
This makes the registration process a few seconds faster.
* solana/Dockerfile: Don't copy devnet_setup.sh at the beginning
This is unnecessary, and inefficient, because each time the file
changes, a lot of things get rebuilt/reinstalled.
* solana/Dockerfile: cache cargo registry
this allows skipping rebuilding cargo dependencies. Small contract
changes now rebuild in 20s, down from 60s before
* Remove unnecessary debian depencies
* Rename rust-toolchain.toml to rust-toolchain (rustup in the container
didn't recognise it with .toml extension) and use in containers
instead of manually specifying rust version
* solana/Dockerfile: Use prebuilt docker image
* solana: Add docs on docker base images
Csongor Kiss