docker: streamline overrides, rename datadirs, external TLS

also
- get rid of CHATMAIL_* in compose
- trim compose override example

docker/files/setup_chatmail_docker.sh

@@ -2,6 +2,8 @@
 
 set -euo pipefail
 export CHATMAIL_INI="${CHATMAIL_INI:-/etc/chatmail/chatmail.ini}"
+export CHATMAIL_NOSYSCTL=True
+export CHATMAIL_NOPORTCHECK=True
 
 CMDEPLOY=/opt/cmdeploy/bin/cmdeploy