docker: adjust php-fpm pool log config on compose

docker/php/www.conf

@@ -1,6 +1,12 @@
 [www]
+access.log = /proc/self/fd/2
+
+; Ensure worker stdout and stderr are sent to the main error log.
+catch_workers_output = yes
+
 user = www-data
 group = www-data
+
 listen = 127.0.0.1:9000
 pm = static
 pm.max_children = 16