Implement subscribe function in Notification controller.

src/controller/mod.rs

 use rocket::fairing::AdHoc;
 
+use crate::model::notification::Notification;
+
 pub mod notification;
 
 pub fn route_stage() -> AdHoc {
     return AdHoc::on_ignite("Initializing controller routes...", |rocket| async {
         rocket
-            .mount("/", routes![])
+            .mount("/", routes![notification::subscribe])
     });
 }

src/controller/notification.rs

@@ -3,4 +3,12 @@ use rocket::serde::json::Json;
 use bambangshop_receiver::Result;
 use crate::model::notification::Notification;
 use crate::model::subscriber::SubscriberRequest;
-use crate::service::notification::NotificationService;
+use crate::service::notification::NotificationService;
\ No newline at end of file
+
+#[get("/subscribe/<product_type>")]
+pub fn subscribe(product_type: &str) -> Result<Json<SubscriberRequest>> {
+    return match NotificationService::subscribe(product_type) {
+        Ok(f) => Ok(Json::from(f)),
+        Err(e) => Err(e)
+    };
+}
\ No newline at end of file