Let go package manager handling go-ethereum and ethermint for build with docker. The difference is that
go-ethereum and ethermint are now public so no need to clone them on-premise for docker build. Another needed update is
the first line of go.mod for both repositories, i.e. replace ethereum by zama-ai in module path.

Another improvement is to use the docker image of fhevm-tfhe-cli for key generation instead of build from source. Still the user can
choose to build the binary from sources by setting the FHEVM_TFHE_CLI_PATH env variable.