Aeternity builder image

The images are automatically published to DockerHub aeternity/builder. It is meant to be used as docker base image for aeternity node builds.

Note: We build and install RocksDB as a dynamically loaded library to speed up aeternity build times. For this to work, -DWITH_SYSTEM_ROCKSDB=ON must be passed when building the erlang-rocksdb bindings. This is set up in the aeternity Dockerfile. Without this flag, erlang-rocksdb will compile and link RocksDB statically, which takes a long time.