Checkmk Werk 15432: agent: GET non existent agent hash now returns a 404 response

ID: 15432 Title: agent: GET non existent agent hash now returns a 404 response Component: REST API Level: 1 Class: Bug fix Version: 2.3.0b1 This werk is to fix an issue when requesting an agent that doesn't exist via the following endpoints GET /objects/agent/non-existing-hash GET /domain-types/agent/actions/download_by_hash/invoke Previously, both of these endpoints would respond with a 500 internal server error, but now we conform to our other endpoints and we return a problem response with an appropriate message.