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/doc/src/feed.rs

@@ -0,0 +1,10 @@
+use api::{models::ApiErrorResponse, routers::feed::*};
+use models::schemas::thought::{ThoughtListSchema, ThoughtSchema};
+use utoipa::OpenApi;
+
+#[derive(OpenApi)]
+#[openapi(
+    paths(feed_get),
+    components(schemas(ThoughtSchema, ThoughtListSchema, ApiErrorResponse))
+)]
+pub(super) struct FeedApi;