tune PHP and FPM for 1-core/3GB VPS performance

Reduce FPM workers from 12 to 5 max to stop memory thrashing on
a single-core VPS with 3GB RAM. Add OPcache and APCu tuning to
reduce filesystem stat calls and improve cache hit rates.

nextcloud/docker-compose.yml

@@ -20,6 +20,7 @@ services:
       - ./hooks/post-installation.sh:/docker-entrypoint-hooks.d/post-installation/post-installation.sh:ro
       - ./hooks/post-upgrade.sh:/docker-entrypoint-hooks.d/post-upgrade/post-upgrade.sh:ro
       - ./fpm-tuning.conf:/usr/local/etc/php-fpm.d/zz-tuning.conf:ro
+      - ./php-tuning.ini:/usr/local/etc/php/conf.d/zz-tuning.ini:ro
     networks:
       - nextcloud-internal
     logging: