[Java][Client] JSON-B serialization support

[djnalluri]

This PR adds JSON-B as a serialization option in the Java client. It is based on the work done in the Microprofile library with the goal of eventually replacing the library-specific templates created there. This is the JSON-B changes from #8716.

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[wing328]

Tested locally and the output compiles without issues.

[wing328]

@djnalluri thanks for the PR, which has been included in the v5.1.0 release: https://twitter.com/oas_generator/status/1373636654024380423