Add Discord outbound posting (#14)

Stacks on #13. Adds discord_post_links and a subscriber that posts roots into a public thread, replies into that thread, and edits the linked Discord message. Unset Discord env leaves the site unchanged.

Reviewed-on: #14
Co-authored-by: codegirl-007 <s.raide@gmail.com>

cmd/server/main.go

@@ -17,6 +17,7 @@ import (
 
 	"plumber"
 	"plumber/internal/blob"
+	"plumber/internal/discord"
 	"plumber/internal/events"
 	"plumber/internal/mail"
 	"plumber/internal/store"
@@ -35,7 +36,15 @@ func main() {
 	if err != nil {
 		log.Fatalf("mail: %v", err)
 	}
-	handler := newHandler(db, sessions, uploader, notifier, events.New())
+	bus := events.New()
+	bot, err := discord.FromEnv(store.NewDiscordLinks(db), bus)
+	if err != nil {
+		log.Fatalf("discord: %v", err)
+	}
+	if bot != nil {
+		defer bot.Close()
+	}
+	handler := newHandler(db, sessions, uploader, notifier, bus)
 	run(&http.Server{
 		Addr:              listenAddr(),
 		Handler:           handler,