release-23.1: changefeedccl: fix initial scan checkpointing

[wenyihu6]

Backport 1/1 commits from #123625.

/cc @cockroachdb/release

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Initially, all span initial resolved timestamps are kept as zero upon resuming a
job since initial resolved timestamps are set as initial high water which
remains zero until initial scan is completed. However, since
0eda540,
we began reloading checkpoint timestamps instead of setting them all to zero at
the start. In PR #102717, we introduced a mechanism to reduce message duplicates
by re-loading job progress upon resuming which largely increased the likelihood
of this bug. These errors could lead to incorrect frontier and missing events
during initial scans. This patches changes how we initialize initial high water
and frontier by initializing it as zero if there are any zero initial high water
in initial resolved timestamps.

Fixes: #123371

Release note (enterprise change): Fixed a bug in v22.2+ where long running
initial scans may incorrectly restore checkpoint job progress and drop events
during node / changefeed restart. This issue was most likely to occur in
clusters with: 1) changefeed.shutdown_checkpoint.enabled (v23.2) is set 2)
Multiple table targets in a changefeed, or 3) Low
changefeed.frontier_checkpoint_frequency or low
changefeed.frontier_highwater_lag_checkpoint_threshold.

---

Release justification: Fixed a severe bug in v22.2+ where long running
initial scans may incorrectly restore checkpoint job progress and drop events
during node / changefeed restart.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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[cockroach-teamcity]

This change is 

[wenyihu6]

blathers backport release-23.1.22-rc