Allow to set initial chown permissions to volume

[shyim]

When you create a docker volume, only the root user can write into it.

It would be nice if we could set initial permissions for a docker volume.

That is what I typically do in my compose:

 init-perm:
        image: alpine
        volumes:
            - files:/var/www/html/files
            - theme:/var/www/html/public/theme
            - media:/var/www/html/public/media
            - thumbnail:/var/www/html/public/thumbnail
            - sitemap:/var/www/html/public/sitemap
        command: chown 82:82 /var/www/html/files /var/www/html/public/theme /var/www/html/public/media /var/www/html/public/thumbnail /var/www/html/public/sitemap

    init:
        image: local
        build:
            context: .
        env_file: .app.env
        entrypoint: /setup
        volumes:
            - files:/var/www/html/files
            - theme:/var/www/html/public/theme
            - media:/var/www/html/public/media
            - thumbnail:/var/www/html/public/thumbnail
            - sitemap:/var/www/html/public/sitemap
        depends_on:
            db:
                condition: service_started
            init-perm:
                condition: service_completed_successfully

[shyim]

whoopsiee https://github.com/basecamp/kamal/issues/897