Create Notification model struct.

src/model/mod.rs

 pub mod product;
 pub mod subscriber;
+pub mod notification;

src/model/notification.rs

+use rocket::serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(crate = "rocket::serde")]
+pub struct Notification {
+    pub product_title: String,
+    pub product_type: String,
+    pub product_url: String,
+    pub subscriber_name: String,
+    pub status: String
+}
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