Feature Request: Add support for secrets when using Docker Compose

[iainchesworth]

When using Docker compose (as described here), the password for the UPS monitor user needs to be passed in via an environment variable in the YAML.

It would be great to be able to use Docker secrets as shown in the Docker documentation to inject the password. Then, passwords would not need to be stored in the Docker compose file; this is a benefit when using GitOps or other CI/CD flows.

Example using Docker secrets:

secrets:
  nut-webgui-password:
    # See https://docs.docker.com/compose/use-secrets/
    file: /home/nut-webgui/nut-webgui-password.txt

services:
  nut-webgui:
    image: ghcr.io/superioone/nut_webgui:latest
    restart: always
    ports:
      - 80:1234
    environment:
      POLL_FREQ: "60"
      POLL_INTERVAL: "5"
      UPSD_ADDR: "myhost"
      UPSD_PORT: "1234"
      UPSD_USER: "admin"
      LISTEN: "0.0.0.0"
      PORT: "1234"
      LOG_LEVEL: "debug"
    secrets:
      - nut-webgui-password

In this example, the UPSD_USER's password would be loaded from /run/secrets/nut-webgui-password