release-22.2: backupccl: incremental schedules always wait on_previous_running

[adityamaru]

Backport 1/1 commits from #98249.

/cc @cockroachdb/release

---

An incremental backup schedule must always wait if there is a running job
that was previously scheduled by this incremental schedule. This is
because until the previous incremental backup job completes, all future
incremental jobs will attempt to backup data from the same StartTime
corresponding to the EndTime of the last incremental layer. In this
case only the first incremental job to complete will succeed, while the
remaining jobs will either be rejected or worse corrupt the chain of
backups.

This change overrides the Wait behaviour for an incremental schedule to
always default to wait during schedule creation or in an alter statement.
Note the user specified value will still be applied to the full backup schedule.

Ideally we'd have a way to configure options for both the full and
incremental schedule separately, in which case we could reject the
on_previous_running configuration for incremental schedules.
Until then this workaround will have to do and we should call out this
known limitation.

Fixes: #96110

Release note (enterprise change): backup schedules created or altered to
have the option on_previous_running will have the full backup
schedule created with the user specified option, but will override the
incremental backup schedule to always default to on_previous_running = wait.
This ensures correctness of the backup chains created by the incremental
schedule by preventing duplicate incremental jobs from racing against each
other.

Release justification: low risk, high impact change

[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