nixos/synapse: move into matrix category

nixos/modules/module-list.nix

@@ -499,6 +499,7 @@
   ./services/mail/roundcube.nix
   ./services/mail/sympa.nix
   ./services/mail/nullmailer.nix
+  ./services/matrix/matrix-synapse.nix
   ./services/matrix/mjolnir.nix
   ./services/matrix/pantalaimon.nix
   ./services/misc/ananicy.nix
@@ -565,7 +566,6 @@
   ./services/misc/matrix-appservice-discord.nix
   ./services/misc/matrix-appservice-irc.nix
   ./services/misc/matrix-conduit.nix
-  ./services/misc/matrix-synapse.nix
   ./services/misc/mautrix-facebook.nix
   ./services/misc/mautrix-telegram.nix
   ./services/misc/mbpfan.nix