Add check constraint, language entry mapping (#497)

* Fix working directory for pgcopydb stream cleanup.

* Add CHECK CONSTRAINT archive entry mapping.

* Fix success return of `copydb_target_finalize_schema` on failure.

* Add CHECK CONSTRAINT unit test

* Add LANGUAGE archive entry mapping

* Link issue in unit test

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Co-authored-by: Shubham Dhama <shubhamdhamaofficial@gmail.com>