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/php-tuning.ini

@@ -0,0 +1,10 @@
+; OPcache tuning for Nextcloud
+opcache.interned_strings_buffer=16
+opcache.max_accelerated_files=10000
+opcache.revalidate_freq=60
+opcache.save_comments=1
+opcache.enable_file_override=1
+
+; APCu local cache
+apc.shm_size=64M
+apc.enable_cli=1