Return correct status codes in process-check-result API

[DamianoChini]

Hi all!

This PR addresses the issue #9353.

fixes #9353

In the implementation we modified the ProcessCheckResult function in order to return an enum that describes the actual result of the function. In the ApiActions::ProcessCheckResult function we check the returned enum and create a result with an appropriate code and status message.
Please let us know if you think other status codes can be more appropriate.

Below you find some curl request with which we can test the changes, in particular to check that the API returns an appropriate reply when we send a process-check-result with an older timestamp with respect to the last check result of the host.

Tests

Initial process-check-result:

curl -v -k -u root:<pwd> 'https://localhost:5665/v1/actions/process-check-result' -H 'accept: application/json' -XPOST -d '{"type": "Host", "host": "my-host", "exit_status": 1, "plugin_output": "initial pcr", "execution_start": "1650553018.000000", "execution_end": "1650553018.000000"}'
should return
{"results":[{"code":200.0,"status":"Successfully processed check result for object 'my-host'."}]}

Process-check-result with older execution_start:

curl -v -k -u root:<pwd> 'https://localhost:5665/v1/actions/process-check-result' -H 'accept: application/json' -XPOST -d '{"type": "Host", "host": "my-host", "exit_status": 1, "plugin_output": "pcr with older timestamp", "execution_start": "1650553017.000000", "execution_end": "1650553017.000000"}'
should return:
{"results":[{"code":409.0,"status":"Newer check result already present. Check result for 'my-host' was discarded."}]}

Process-check-result with newer execution_start:

curl -v -k -u root:<pwd> 'https://localhost:5665/v1/actions/process-check-result' -H 'accept: application/json' -XPOST -d '{"type": "Host", "host": "my-host", "exit_status": 1, "plugin_output": "pcr with newer timestamp", "execution_start": "1650553019.000000", "execution_end": "1650553019.000000"}'
should return:
{"results":[{"code":200.0,"status":"Successfully processed check result for object 'my-host'."}]}

[DamianoChini]

Hi @julianbrost !
Thank you very much for the fast reply, I pushed the changes as per you feedback.
Sorry for the multiple pushes to the branch, I keep forgetting setting my IDE to use tabs instead of whitespaces for indentation :)

[julianbrost]

I didn't consider how long the names would get when moving the enum into the class. I suggest adding using Result = Checkable::ProcessingResult; to ApiActions::ProcessCheckResult() and Checkable::ProcessCheckResult() and then using that alias to keep things a bit shorter.

[julianbrost]

Just one tiny indentation mishap left to fix, then I'm happy with the PR.

[Al2Klimov]

A little bit over-engineered, but better than the other way around.

@julianbrost Also see my OP edit.