fix(mailcow): Following mailcow's example we'll use TZ as our timezone var env var instead of TIMEZONE

mailcow/env/fully.qualified.domain.name.example

@@ -1,8 +1,8 @@
 # Feel free to leave defaults. They apply while these vars are commented out
 # ---
 # RESTARTPOLICY=unless-stopped
-# TIMEZONE=Etc/UTC
-TIMEZONE=<user_defined_value>
+# TZ=Etc/UTC
+TZ=<user_defined_value>
 
 # Unbound, redis, clamd, rspamd, php-fpm, SOGo, dovecot, Postfix, Nginx, acme, netfilter, watchdog, dockerapi
 IPV4_NETWORK=<user_defined_value>