Build with S6 (bullseye)

The changes include recent ModSecurity-CRS rules, that make the Gutenberg editor work.

docker/conf/chaperone.d/clean-sessions.service

-clean_sessions.service: {
-    type: cron,
-    interval: "10,40 * * * *",
-    command: "/usr/bin/find /var/lib/php/sessions -mindepth 1 -type f -mtime +1 -delete",
-}