release-23.1: kvserver: deflake TestPromoteNonVoterInAddVoter

[kvoli]

Backport 1/2 commits from #103083.

/cc @cockroachdb/release

---

It is possible for span config updates to arrive at different times
between stores. TestPromoteNonVoterInAddVoter was flaking when the
incoming leaseholder would act upon a stale span config, before
receiving the updated one which the outgoing leaseholder used.

This resulted in the test failing as more than just the two expected
promotion events appeared in the range log, as the incoming leaseholder
removed voters, then subsequently added them back upon receiving the
up to date span configuration.

#103086 tracks this issue.

This PR checks on the prefix of the range log add voter events, to
avoid failing the test when this untimely behavior occurs.

Stressed overnight, removing the skip under stress flag:

dev test pkg/kv/kvserver -f TestPromoteNonVoterInAddVoter -v --stress --stress-args="-p 4"
...
27158 runs so far, 0 failures, over 12h56m55s

This PR also adds additional (v=6) logging of the range descriptor and span config,
as these come in handy when debugging failures such as this.

Fixes: #101519

Release note: None

---

Informs: #105883
Release justification: Test only 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 

[kvoli]

TYFTR