[Postfix] Use Redis master if set

data/Dockerfiles/postfix/syslog-ng-redis_slave.conf

@@ -0,0 +1,49 @@
+@version: 3.19
+@include "scl.conf"
+options {
+  chain_hostnames(off);
+  flush_lines(0);
+  use_dns(no);
+  dns_cache(no);
+  use_fqdn(no);
+  owner("root"); group("adm"); perm(0640);
+  stats_freq(0);
+  bad_hostname("^gconfd$");
+};
+source s_src {
+  unix-stream("/dev/log");
+  internal();
+};
+destination d_stdout { pipe("/dev/stdout"); };
+destination d_redis_ui_log {
+  redis(
+    host("`REDIS_SLAVEOF_IP`")
+    persist-name("redis1")
+    port(`REDIS_SLAVEOF_PORT`)
+    command("LPUSH" "POSTFIX_MAILLOG" "$(format-json time=\"$S_UNIXTIME\" priority=\"$PRIORITY\" program=\"$PROGRAM\" message=\"$MESSAGE\")\n")
+  );
+};
+destination d_redis_f2b_channel {
+  redis(
+    host("`REDIS_SLAVEOF_IP`")
+    persist-name("redis2")
+    port(`REDIS_SLAVEOF_PORT`)
+    command("PUBLISH" "F2B_CHANNEL" "$MESSAGE")
+  );
+};
+filter f_mail { facility(mail); };
+# start
+# overriding warnings are still displayed when the entrypoint runs its initial check
+# warnings logged by postfix-mailcow to syslog are hidden to reduce repeating msgs
+filter f_overrides { not match("overriding earlier entry" value("MESSAGE")); };
+# end
+filter f_skip_local { not facility (local0, local1, local2, local3, local4, local5, local6, local7); };
+log {
+  source(s_src);
+  filter(f_skip_local);
+  filter(f_overrides);
+  destination(d_stdout);
+  filter(f_mail);
+  destination(d_redis_ui_log);
+  destination(d_redis_f2b_channel);
+};