_cq_pg_cdc_event_time for long lived processes

[smylbb]

Which problem is this feature request solving?

Currently for long lived syncing processes like postgres CDC mode sync, the _cq_sync_time reflects the time that the process began which causes issues of duplication with destinations such as clickhouse which could have otherwise been resolved with ReplacingMergeTree at merge time.

Describe the solution you'd like

Add a dynamic sync time as a separate column in the cdc mode, something like "_cq_pg_cdc_event_time", which clickhouse will use to determine the most recent record to keep at merge time.

Pull request (optional)

• I can submit a pull request

[bbernays]

I think this is a duplicate of #15690