Return all day off recorded for given month and person.
GET
/data/persons/{person_id}/day-offs/month/{year}/{month}
GET /data/persons/{person_id}/day-offs/month/{year}/{month}
curl \
-X GET http://localhost:8080/api/data/persons/{person_id}/day-offs/month/{year}/{month} \
-H "Authorization: $API_KEY"