TIKA-4355 -- LibPstParserConfig should be serializable

[tballison]

Thanks for your contribution to Apache Tika! Your help is appreciated!

Before opening the pull request, please verify that

• there is an open issue on the Tika issue tracker which describes the problem or the improvement. We cannot accept pull requests without an issue because the change wouldn't be listed in the release notes.
• the issue ID (TIKA-XXXX)
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