create health check route

[bernardev254]

Add Health Check Endpoint

Description

This PR introduces a /health endpoint to the Axum server to provide a simple way to verify the server's status. The endpoint responds with a JSON payload:
{ "status": "ok" }

Changes Made

• Added a new route /health that responds to GET requests.
• Implemented a health_check handler to return the JSON response.
• Updated dependencies in Cargo.toml to include serde_json for JSON serialization.
  closes Add Health Check Endpoint #5