Add multi user auth (private mode only)

[MotorTruck1221]

TODO:

• Add basic DB connection
• Authenticate multiple users
• CLI to add, delete, list, and reset password
• Make basic DB connection configurable (ENV and config.yml)
• Update example config to reflect changes
• Update docker compose
• Update docs to reflect changes

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Other Changes

• mainURL is now not required in private mode and can be deleted