Optimize Docker build

[charlesjliu]

At the moment, the docker image for the api is generated by copying the src/ files to the docker image, installing all the packages (devDependencies too) and running babel in the container on the src/ files, before running the server.

This is a bloated process that can be streamlined with the help of a preliminary step that generates a builder image: https://medium.com/@guillaumejacquart/node-js-docker-workflow-12febcc0eed8

Acceptance Criteria

• the built docker image with the server on it does not contain unnecessary files/dependencies
• docker-compose will still spin up the server for first time devs