nextcloud: Limit Nginx Paths access to relevant directories only

[JGoutin]

Currently have full access to the /var/www/nextcloud directory. Some paths are restricted in the Nginx configuration, but should be blocked by systemd especially config that contains sensitive data.

From Nginx configuration:

location ~ ^/(?:build|tests|config|lib|3rdparty|templates|data)(?:$|/)  { return 404; }
location ~ ^/(?:\.|autotest|occ|issue|indie|db_|console)                { return 404; }