feat(panettone): announce newly created issues using irccat

- The new PANETTONE.IRC package contains the SEND-IRC-NOTIFICATION function,
  which opens a new TCP socket to irccat (if it's running and configured) in
  order to announce the creation of new issues.
- The IRCCATHOST and IRCCATPORT environment variables must be set for this to
  work.
- Additionally, the ISSUECHANNEL environment variable may be used to direct
  announcements at a given channel (otherwise it'll just use the first one).

Change-Id: I429a66f24d0f80ed10db173d6af7105fb1d3d023
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2077
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

web/panettone/default.nix

@@ -26,6 +26,7 @@ depot.nix.buildLisp.program {
     ./src/css.lisp
     ./src/authentication.lisp
     ./src/model.lisp
+    ./src/irc.lisp
     ./src/panettone.lisp
   ];