fix: Block duplicate status code definitions

[provokateurin]

Duplicate status code definitions lead to invalid specs (https://github.com/julien-nc/cospend-nc/blob/76964a296fd1a22aabf147e3fec5dec0b48fd4eb/openapi.json#L7939) because they can not be merged automatically. Therefore we need to prevent people from defining a status code twice. IMO this also lines up with HTTP semantics were one status code always means a specific body and set of headers is returned. It is up to the developer to specify the body and header types correctly (e.g. nullability).

[nickvergessen]

PHP Fatal error: Uncaught Error: OCM#discovery: Each status code can only be defined once, but 2 was defined multiple times.
thrown in /home/runner/work/openapi-extractor/openapi-extractor/src/Logger.php on line 53

[nickvergessen]

Ah, that's "implicit", one 500 is documented as it's returned, one is automatic because it's from an exception

[provokateurin]

I see, also the error message is wrong because it should have shown the status code and not the number of times it appears.

[provokateurin]

For the failure seen in the CI the cause wasn't the 500s, but this PR can't actually work for scenarios where multiple different response classes are used like in https://github.com/nextcloud/server/blob/489608a2238a62409eb2305a2aee621d6bd774b6/apps/theming/lib/Controller/IconController.php#L117.
The proper fix for that would be to allow different content types to define the same status code, but that also doesn't work for the case mentioned above because of the different response classes.
I don't see another way than printing a warning about this case (every time) and panic in case an invalid spec would be generated.
@nickvergessen what are your thoughts?