Upvote a request

curl -X POST "http://localhost:3000/api/v1/requests/req_123456789/upvote" \
  -H "x-request-kit-key: <string>" \
  -H "Content-Type: application/json" \
  -d '{
    "user": {
      "identifier": "user123",
      "name": "John Doe",
      "email": "john@example.com"
    }
  }'