Update health API to pass authenticated users their info

This allows Khoj clients to get email address associated with
user's API token for display in client UX

In anonymous mode, default user information is passed

src/khoj/routers/api.py

@@ -554,6 +554,8 @@ async def extract_references_and_questions(
     return compiled_references, inferred_queries, defiltered_query
 
 
-@api.get("/health")
-async def health_check():
-    return Response(status_code=200)
+@api.get("/health", response_class=Response)
+@requires(["authenticated"], status_code=200)
+def health_check(request: Request) -> Response:
+    response_obj = {"email": request.user.object.email}
+    return Response(content=json.dumps(response_obj), media_type="application/json", status_code=200)