Support --env-file flag for docker compose usage

Currently the devcontainer.json spec does not allow for me to specify an .env file for usage in the CLI:
https://docs.docker.com/compose/environment-variables/set-environment-variables/#substitute-with---env-file

This would be really useful, as I currently cannot rely on a root .env file as suggested by the docs, due to collisions with other devs/IDEs and a desire to not pollute each other's ways of working, yet would still like to make use of env var substitution features inside of common .yml files whenever I am running them through the devcontainer stack