fix: add on delete cascade to notifications and userNotifications tables (#3192)

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Signed-off-by: andreas-unleash <andreas@getunleash.ai>

src/migrations/20230222154915-create-notiications-table.js

@@ -5,15 +5,15 @@ exports.up = function (db, cb) {
         `
             CREATE TABLE IF NOT EXISTS notifications (
                  id SERIAL PRIMARY KEY,
-                 event_id INTEGER NOT NULL REFERENCES  events (id),
-                 created_by INTEGER NOT NULL REFERENCES  users (id),
+                 event_id INTEGER NOT NULL REFERENCES  events (id) ON DELETE CASCADE,
+                 created_by INTEGER NOT NULL REFERENCES  users (id) ON DELETE CASCADE,
                  created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT now()
             );
 
             CREATE TABLE if not exists user_notifications
             (
-                notification_id INTEGER NOT NULL REFERENCES notifications (id),
-                user_id         INTEGER NOT NULL REFERENCES  users (id),
+                notification_id INTEGER NOT NULL REFERENCES notifications (id) ON DELETE CASCADE,
+                user_id         INTEGER NOT NULL REFERENCES  users (id) ON DELETE CASCADE,
                 read_at         TIMESTAMP WITH TIME ZONE,
                 PRIMARY KEY (notification_id, user_id)
             );