DevExp: local environment

[khvn26]

This is a tracking issue for current problems when trying to bring up Flagsmith locally:

cc @gnumoreno

Common

• [ ] No single documented way of doing this. We should also document prerequisites i.e. pyenv, Docker and npm.

API

• [ ] make install failing due to Poetry not updating $PATH out of the box.
• [ ] make serve target should invoke docker-up and django-migrate targets automatically.

Frontend

• [ ] make build target is incorrect, should invoke npm run bundle instead of npm run build.
• [ ] Should add ENV=local to .env-local to point frontend brought up by the make serve target to the local API.