[JAVA][jersey2] import the auto generated supporting JSON class only when discriminator is needed

[beytun]

Import the auto generated supporting JSON class only when generateSupportingFiles is true and discriminator is needed.

The similar issue #8027 was fixed with PR #8554 for JAVA native client. This PR fixes the issue for JAVA jersey2 client.

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@bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608 @nmuesch

[beytun]

cc: @agilob @wing328

[wing328]

LGTM

[wing328]

@beytun we've to revert this change via #10597 as it's breaking the build due to anyOf/oneOf also needs the JSON class.

For the error message , please refer to https://app.circleci.com/pipelines/github/OpenAPITools/openapi-generator/13254/workflows/f53036aa-5cfe-4fd0-876e-f98464acd1cf/jobs/26909