WIP : Docker image optimizations

[ymoisan]

• [ ] Copying CONDA_DIR from stage 1 takes more than 10 GB of temporary disk space; investigate
• [x] Build using our GitHub repo as (remote) context docker build https://github....git#branch|tag|remote_referencer:optional_dir ¹
• [ ] Create a .dockerignore file (aka don't ship unnecessary files to the build context)
• [ ] Build a "swiss-army knife" dockerfile to "make sure that you, your team, and the CI are all using the same environment" ²

¹ Build from a url instead of a local context; when the URL parameter points to the location of a Git repository, the repository acts as the build context. The system recursively fetches the repository and its submodules. The commit history is not preserved. docker build ² Containerize Your Go Developer Environement, part 2