feature addition: docker image supporting PUID/PGID

[march42]

I am running eclipse-mosquitto in docker, using a modified image with support for setting PUID/PGID.

• The image is based on 2.1-alpine.
• Package daemontools-encore provides needed setuidgid
• Package shadow provides needed groupmod and usermod
• docker-entrypoint.sh
  • modifies GID of group mosquitto
  • modifies UID and primary GID of user mosquitto
  • changes ownership of /mosquitto
  • starts configured CMD (rely on mosquitto dropping root privileges)
• fixes Add Support for PGID and PUID Docker Enviroment Variables #2441

For testing, the current image can be pulled from Docker hub image marchefter/eclipse-mosquitto:appuser.

services:
  mosquitto:
    image: marchefter/eclipse-mosquitto:appuser
    healthcheck:
      test: ["CMD-SHELL", "/usr/bin/mosquitto_sub -C 1 --topic '$$SYS/broker/uptime' 2>/dev/null || exit 1"]
    environment:
      TZ: "Europe/Berlin"
      PUID: 2388
      PGID: 1763
    ports:
      - "1883:1883" # default mqtt port
      - "8883:8883" # mqtt TLS port
    volumes:
      - ./mosquitto_config:/mosquitto/config
      - ./mosquitto_data:/mosquitto/data
      - ./mosquitto_log:/mosquitto/log