Feature request: ability to add a custom Apache docroot

Working with the `8.2-apache` image - is there a way to specify a docroot in the apache config that is different than `/var/www/html` ? Using Symfony, the docroot is in a `public` sub directory, rather than at the same level as the mounted files; something like:

```
...
- APACHE_SERVER_NAME=my-site.local
- APACHE_SERVER_ALIAS=*.my-site.local
- APACHE_SERVER_DOCROOT=/var/www/html/public
```

    