Modifying schema-sync implementation to use polling for OSS/Pro. Invalidations are now propagated via the `hdb_catalog.hdb_schema_notifications` table in OSS/Pro. Pattern followed is now a Listener/Processor split with Cloud listening for changes via a LISTEN/NOTIFY channel and OSS polling for resource version changes in the metadata table. See issue #460 for more details.
GitOrigin-RevId: 48434426df02e006f4ec328c0d5cd5b30183db25