Update created_at to return a timestamp.

src/controllers/user.rs

@@ -69,6 +69,6 @@ fn response_user(user: User) -> dto::user::ResponseUser {
     dto::user::ResponseUser {
         id: user._id.unwrap().to_string(),
         email: user.email,
-        created_at: user.created_at.to_string()
+        created_at: user.created_at.timestamp_millis()
     }
 }

src/dto/user.rs

@@ -11,5 +11,5 @@ pub struct Login {
 pub struct ResponseUser {
     pub id: String,
     pub email: String,
-    pub created_at: String
+    pub created_at: i64
 }