feat(nixos/clbot): Add ability to post in multiple channels

Adds the ability to post to multiple channels by simply running
multiple instances of clbot.

We should probably implement support for this in clbot itself, but
right now I can't be bothered to write Go.

Change-Id: I5cffd0dc10a7f6cc19c37c5834c5610166b4ae23
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1771
Tested-by: BuildkiteCI
Reviewed-by: kanepyork <rikingcoding@gmail.com>
Reviewed-by: lukegb <lukegb@tvl.fyi>

ops/nixos/whitby/default.nix

@@ -218,6 +218,11 @@ in lib.fix(self: {
       # populated from /etc/secrets/clbot
       irc_pass = "$CLBOT_PASS";
     };
+
+    channels = [
+      "##tvl"
+      "##tvl-dev"
+    ];
   };
 
   services.depot = {