[WEB-6420] chore: migrate community references from Discord to Forum (#8657)

* chore: replace Discord references with Forum links

* chore: migrate help and community CTAs from Discord to Forum

* refactor: replace Discord icons with lucide MessageSquare

* chore: rename Discord labels and keys to Forum

* chore: remove obsolete Discord icon component

* chore: update Discord references to Forum in templates

* chore: code refactoring

apps/space/app/error.tsx

@@ -24,13 +24,8 @@ function ErrorPage() {
               support@plane.so
             </a>{" "}
             or on our{" "}
-            <a
-              href="https://discord.com/invite/A92xrEGCge"
-              target="_blank"
-              className="text-accent-primary"
-              rel="noopener noreferrer"
-            >
-              Discord
+            <a href="https://forum.plane.so" target="_blank" className="text-accent-primary" rel="noopener noreferrer">
+              Forum
             </a>
             .
           </p>