feat: Implement WebFinger discovery and ActivityPub user actor endpoint

- Added a new router for handling well-known endpoints, specifically WebFinger.
- Implemented the `webfinger` function to respond to WebFinger queries.
- Created a new route for WebFinger in the router.
- Refactored user retrieval logic to support both user ID and username in a single endpoint.
- Updated user router to use the new `get_user_by_param` function.
- Added tests for WebFinger discovery and ActivityPub user actor endpoint.
- Updated dependencies in Cargo.toml files to include necessary libraries.

thoughts-backend/Cargo.toml

@@ -19,7 +19,7 @@ axum = { version = "0.8.4", default-features = false }
 sea-orm = { version = "1.1.12" }
 sea-query = { version = "0.32.6" }                              # Added sea-query dependency
 serde = { version = "1.0.219", features = ["derive"] }
-serde_json = { version = "1.0.140" }
+serde_json = { version = "1.0.140", features = ["raw_value"] }
 tracing = "0.1.41"
 utoipa = { version = "5.4.0", features = ["macros", "chrono"] }
 validator = { version = "0.20.0", default-features = false }