Docker compose user settings from .env or defaults

[lperson]

Description

Have the docker compose file look for settings in .env and use defaults if they are not present.

This is a convenience for local development. If someone is working on multiple projects, this will enable them to run multiple instances of postgres and redis on their local machine.

The relevant entries in my .env file are

REDIS_PORT=16379
DB_USER=spokedev
DB_PORT=15432
DB_NAME=spokedev
DB_PASSWORD=spokedev

Checklist:

• I have manually tested my changes on desktop and mobile
• The test suite passes locally with my changes
• If my change is a UI change, I have attached a screenshot to the description section of this pull request
• My change is 300 lines of code or less, or has a documented reason in the description why it’s longer
• I have made any necessary changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• My PR is labeled [WIP] if it is in progress