nixos/zoneminder: also run zmupdate "freshen" on start

-f "freshen the configuration in the database", which will matter when
ZoneMinder adds a new configuration item [1]. Although it can also be
run without a new configuration item too; upstream's Debian postinst
code always run it on upgrade [2].

[1] e.g. https://forums.zoneminder.com/viewtopic.php?p=127220
[2] https://github.com/ZoneMinder/zoneminder/blob/master/distros/ubuntu2004/zoneminder.postinst#L45

nixos/modules/services/misc/zoneminder.nix

@@ -326,6 +326,7 @@ in {
           fi
 
           ${zoneminder}/bin/zmupdate.pl -nointeractive
+          ${zoneminder}/bin/zmupdate.pl --nointeractive -f
         '';
         serviceConfig = {
           User = user;