[Commands] Cleanup #shutdown Command (#3830)

# Notes
- Cleanup messages and logic.
- Add a confirmation so operators don't accidentally shutdown the zone they're in thinking this is `#worldshutdown` instead.

zone/gm_commands/shutdown.cpp

@@ -3,6 +3,22 @@
 
 void command_shutdown(Client *c, const Seperator *sep)
 {
-	CatchSignal(2);
+	const int arguments = sep->argnum;
+	if (!arguments) {
+		c->Message(
+			Chat::White,
+			fmt::format(
+				"Using this command will shut down your current zone. Please {} this is what you want to do.",
+				Saylink::Silent("#shutdown confirm", "confirm")
+			).c_str()
+		);
+		return;
 	}
 
+	const bool is_confirm = !strcasecmp(sep->arg[1], "confirm");
+
+	if (is_confirm) {
+		c->Message(Chat::White, "Shutting down your current zone.");
+		CatchSignal(2);
+	}
+}