feat: allow --user option

[asbiin]

This close #42

You can test it either by

1. Using --user flag
   This will require to mount a volume to /var/www/html/storage, so the specified user can write in it (required by Laravel).
   You also need to set APP_KEY environment variable (.env file will not be writable)

2. Setting APACHE_RUN_USER and APACHE_RUN_GROUP environment variable to an existing user name
   This defines the user and group used to run apache (if you use fpm, try scenario 1)

Limitation: the artisan config:cache will not work with scenario 1.