Jersey2/3: Allow multiple MIME-types in Accept-Header (WIP)

[jheyens]

In case of an endpoint that may reply with multiple Content-Types where one of them matches a regex checking for JSON-MIME-types (e.g. a file as application/octet-stream if successful and an error message as application/json in case of an error), the Jersey code will ignore all non-JSON MIME-types. This is an issue if the REST-server checks whether user agents are even able to handle the response format by evaluating the "Accept: "-request header (which it should).

I consider this PR a WIP, since there might be reasons for ignoring non-JSON types that I am not aware of.
There also seems to be an issue with three of the petstore samples not being able to handle application/xml (e.g. https://github.com/DIaLOGIKa-GmbH/openapi-generator/actions/runs/18501770033/job/52720236107). I'ld like a discussion on why other MIME-types are discarded and how we could resolve both of these issues.

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[wing328]

thanks for the PR

can you please update the tests so that the CI tests will pass?

[jheyens]

Unfortunately, not directly, since there is still an issue:

• Without this patch, the generator erroneously drops additional content types if application/json (or equivalent) is present. For resources that provide multiple content types (e.g. a HTTP resource for downloading a file would have a content type of application/octet-stream for a successful request, but could provide a JSON object containing an error message with content type application/json in case of failures)
• With this patch, however, e.g. this test fails, since the PetStore receives a Content-Type: <application/json,application/xml>, then chooses XML, which results in a missing sub element (category; see here) in the response. I haven't investigated (though I assume another bug in openapi-generator when using jersey/JAXB here) yet whether this is an issue in the client or in the Petstore, but the failing tests where written with JSON messages in mind. I am not comfortable fixing this without prior discussion about whether the tests should even be allowed use XML messages instead of JSON.