Process-check-result API should return whether the process-check-result was processed or discarded

[DamianoChini]

Hi all

Is your feature request related to a problem? Please describe.

When executing a process-check-result via Icinga API, we need to understand if the process-check-result was actually processed by Icinga 2 or if it was discarded due to an execution_start older than the last_check_result of the object.
Currently when the process-check-result is discarded, the API returns anyway the following message, which cannot be distinguished from the case where the process-check-result was processed.
{"results":[{"code":200.0,"status":"Successfully processed check result for object '<object_name>'."}]}

Describe the solution you'd like

The Icinga process-check-result API should return a different status code if the event was not processed, with a clear error message.

Additional context

Our use case is that all events occurring on an Icinga 2 object must be somehow reconstructible. We have the history of the events in the Icinga IDO, but this misses those process-check-results that are discarded by the Icinga API due to an execution_start older than the current object's last_check_result. Having the process-check-result API telling us whether the event was processed or discarded, would allow our client to handle the discarding (for example by logging somewhere the discarding of the event).