Use fpm image for Nextcloud
We are having some performance problems on ecloud.global, probably related to Apache which is included in the Nextcloud Docker image, and sometimes goes to 100% CPU usage for no reason. Using fastCGI instead should use less CPU and RAM while speeding up responses.
I already got this working on a test server, and subjectively, it felt much faster than with the current configuration. But right now it seems to be broken for some reason.
I also need to check if more nginx config items are needed (eg deny access to data folder).