[BUG] undocumented but exposed attributes break the java-client

[grafjo]

If the lago-api returns undocumented attributes but those are missing in the open-api spec, causes the lago-java-client to throw exceptions during deserialization of responses.

I expect that lago-java-client ignores unknown attributes in the response-body during deserialization.

Background of this issue is getlago/lago-api#1585