[YSQL] Incrementally refresh PG backend catcaches

[kai-franz]

Jira Link: DB-12688

Description

Currently, whenever a DDL bumps the catalog version, all the PG backend processes throw away and reload their entire catalog cache. Instead, we'd like them to refresh their caches incrementally, pulling in only the rows that have been changed by the DDL.

Issue Type

kind/enhancement

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