release-22.1: changefeedcc: De-flake changefeed tests

[miretskiy]

Backport 1/1 commits from #84109.

/cc @cockroachdb/release

---

Address multiple source of flakes in changefeed tests.

#83530 made a change
to ensure that changefeed do not fail when they are in the transient
(e.g. pause-requested) state. Unfortunately, the PR made a mistake
where even if the checkpoint could not be completed because
the cangefeed is in the "pause requested" state, we would still
proceed to emit resolved event. This is wrong, and the resolved
event should never be emitted if we failed to checkpoint.

In addition, alter changefeed can be used to add new tables to existing
changefeed, with initial scan. In such cases, the newly added table
will emit events as of the timestamp of "alter changefeed statement".
When this happens, the semantics around resolved events are murky
as documented in #84102
Address this issue by making cloud storage sink more permissive around
its handling of resolved timestamp.

When completing initial scan for newly added tables, fix an "off by 1"
error when frontier was advanced to the next timestamp.
This was wrong since #82451
clarified that the rangefeed start time is exclusive.

Informs #83882
Fixes #83946

Release Notes: None
Release Justification: deflake 22.1 release branch.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is