fix(docker-compose): fix and style improvements

#

# SPDX-License-Identifier: CC0-1.0

version: "3.6"

x-common-env: &common-env

  TRAVELYNX_DB_HOST: database

  TRAVELYNX_DB_NAME: travelynx

  TRAVELYNX_DB_USERNAME: travelynx

  TRAVELYNX_DB_PASSWORD: travelynx

  TRAVELYNX_SECRET: 12345678

  TRAVELYNX_MAIL_DISABLE: 1

  MOJO_MODE: development

x-common-config: &common-config

  volumes:

    - ./examples/docker/travelynx.conf:/app/travelynx.conf

  build: .

  networks:

    - backend

services:

  database:

    image: postgres:11

    networks:

      - backend

    environment: 

      <<: *common-env

    volumes:

      - ./examples/docker/postgres-init.sh:/docker-entrypoint-initdb.d/init.sh

  travelynx:

    <<: *common-config

    build: .

    volumes:

      - ./travelynx.conf:/app/travelynx.conf

      - ./travelynx-conf:/app/local

    ports:

      - "8000:8093"

    environment:

      <<: *common-env

      - 127.0.0.1:8000:8093

    links:

      - db

    restart: unless-stopped

  cron:

    <<: *common-config

    environment:

      <<: *common-env

      CRON: 1

    build: .

    volumes:

      - ./travelynx.conf:/app/travelynx.conf

      - ./travelynx-conf:/app/local

    command: worker

    links:

      - db

    restart: unless-stopped

  db:

    image: postgres:17

    env_file: db.env

    volumes:

      - ./db-data:/var/lib/postgresql/data

    restart: unless-stopped

networks:

  backend: