Create Notification database and Notification repository struct skeleton.

src/repository/mod.rs

+pub mod notification;
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src/repository/notification.rs

+use std::sync::RwLock;
+
+use lazy_static::lazy_static;
+
+use crate::model::notification::Notification;
+
+// Singleton of Database
+lazy_static! {
+    static ref NOTIFICATIONS: RwLock<Vec<Notification>> = RwLock::new(vec![]);
+}
+
+pub struct NotificationRepository;
+
+impl NotificationRepository {
+}
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