Create SubscriberRequest model struct.

src/model/mod.rs

+pub mod subscriber;

src/model/subscriber.rs

+use rocket::serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(crate = "rocket::serde")]
+pub struct SubscriberRequest {
+    pub url: String,
+    pub name: String,
+}