[Feature]: Improve process-check-result API error response handling #46

Describe the feature request

while testing #45 i ran across the issue that the objects in icinga where not updated. as it turns out, the Icinga client implementation for the process-check-result API only handles status codes 503, 404, and 200; i received a status code 400, which was silently dropped by the client.

for reference, this was the data the bridge sent to the Icinga2 API

{
  "exit_status": 2,
  "plugin_output": "Host down",
  "ttl": 0,
  "filter": "host.name==\"gaff.bac.test\"",
  "type": "Host"
}

the Icinga2 API responded with the following payload

{
  "results": [
    {
      "code": 400,
      "status": "Invalid 'exit_status' for Host gaff.bac.test."
    }
  ]
}

the cause of the error is not relevant for the moment, but i would at least like to see it propagated to the caller so it can be handled (e.g. logged)

i can provide an MR with the required changes