Added ability to ignore unrecognized hints instead of rasing error

[WinterUnicorn]

We have hints that are used by another extension or hints that are used by an external applications(outside of the database layer). We also have cases when some queries using hints from future versions of pg_hint_plan that are not yet supported in the current version. For example we don't have the "memoize" hint in Postgres 13 but some queries already use this hint because that queries was prepared for a future migration to the Postgres 14.

This feature will add the GUC pg_hint_plan.ignore_unrecognized_hints

The property allows to ignore unrecognized keywords without raising error and continue parsing other hints.