Working concept with news + eelo theme

This MR introduces the possibility of deploying custom apps (with patches, like for Notes) and our theme with the image. It does it with a custom entrypoint that, for now, always run regardless of the server and image versions (should probably be improved).

This simplifies the process of deploying new theme versions; we can just fetch a given nextcloud-theme tag and make sure all changes are included with the right permissions.

I'm not sure it's needed but we can bump the fourth version number so we can deploy these changes as updates even if there is no new NC image available.

I was surprised to see that the upgrade screen appeared in NC, had to click the button. So maybe we don't have to change the version.php at all when only apps/themes change:

Also: the theme was disabled in config.php, as you can see above. I had to add it back in config.php. Not sure this will always happen, but maybe I need to put the instance manually in maintenance with occ from the entrypoint, WDYT?