release-23.2: kvserver: gate writing the new sticky GCHint

[blathers-crl]

Backport 3/3 commits from #112948 on behalf of @pavelkalinnikov.

/cc @cockroachdb/release

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This PR makes the new behaviour of GCHint introduced in #110078 conditional on a default-off cluster setting in 23.1, and enabled in 23.2 by a version gate.

Since it is late to enable this behaviour in 23.1 (risk of backwards incompatibility), hide it behind a default-off cluster setting. In 23.2, it will be enabled by default, and the cluster setting will be deprecated.

The new GCHint behaviour is likely backwards compatible, but we are hiding it behind a setting for extra safety.

The safest moment to enable this cluster setting is when there is some confidence that the cluster binaries will not rollback to previous patch versions of 23.1. The risk exists only in mixed-version state in which some 23.1 binaries don't know the new GCHint fields, and some do.

Epic: none

Release note (ops change): introduce a default-off cluster setting kv.gc.sticky_hint.enabled which helps expediting garbage collection after range deletions, such as when a SQL table or index is dropped.

Release note (general change): set the default behaviour for kv.gc.sticky_hint.enabled cluster setting to enabled since 23.2. The setting is deprecated in 23.2 going forward.

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Release justification: safety net for a critical bug fix

[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?

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[dt]

do we need the setting for this one? can we default on for 23.2 with an IsActive(V_23_2) version gate instead?

[erikgrinaker]

We do, the setting is there to respect it in mixed-version clusters until the upgrade finalizes.