Add support for .env files and setup for database info

[knazir]

Description

Just picked up this project to experiment. While working, I noticed that I kept having to ignore checking in changes to config.yaml that had my plaintext MySQL password.

To make local development a bit safer and more convenient, this adds support for environment variables via a .env file. It also adds a .env.example file in the repo root that demonstrate supported parameters.

Done through an EnvironmentManager class with some helpers.

If I missed an existing/better way to do this, please let me know.

Checklist before requesting review

• Performed a self-review of the code
• Tested changes locally
• Added unit tests where applicable