feat: implement user follow/unfollow functionality and thought retrieval by user

- Added follow and unfollow endpoints for users.
- Implemented logic to retrieve thoughts by a specific user.
- Updated user error handling to include cases for already following and not following.
- Created persistence layer for follow relationships.
- Enhanced user and thought schemas to support new features.
- Added tests for follow/unfollow endpoints and thought retrieval.
- Updated frontend to display thoughts and allow posting new thoughts.

thoughts-backend/utils/src/testing/api/mod.rs

@@ -19,3 +19,15 @@ pub async fn make_post_request(app: Router, url: &str, body: String) -> Response
     .await
     .unwrap()
 }
+
+pub async fn make_delete_request(app: Router, url: &str) -> Response {
+    app.oneshot(
+        Request::builder()
+            .method("DELETE")
+            .uri(url)
+            .body(Body::empty())
+            .unwrap(),
+    )
+    .await
+    .unwrap()
+}