@nebulon my bootstrap script gets you until the install form where the user will be prompt under HTTP to submit account details to proceed with the installation. It doesn't carry the installation as that process has account limitations (password length enforcement, forbidden usernames) but if you want to automate that bit you could simply detect the first run based on the container placeholder and execute the submitInstall installer command.
The installation at that step is just build the database, it doesn't touch the filesystem. As you may noticed, I left the installer.php available to use it as tooling on top of the images look at /chevereto folder in the container.
I suggest you to implement Chevereto on Cloudron using/forking my Docker images as I will constantly maintaining it, specially in regards to the PHP provisioning. That's why I provide separately Apache and PHP-FPM images, so you stop worrying about PHP regardless which flavor you like better. Use
php-fpm if you want to handle the server, simply plug the process. Use Apache HTTP if you want to rely in
Regarding your implementation, I can't recommend to use linking for the
app/settings.php file, I recommend you to use env variables for that purpose. If user needs to sneak a setting it should be made by overriding the env variables, not working on the same file used for app/settings.php dist. If the user needs to add something at "settings level" it should be made with a file made for that sole purpose.