release-25.2: kvcoord: make kv.transaction.write_buffering.enabled non-public

[stevendanna]

This feature should likely only be used in newer release, removing it from the list of cluster settings makes it more clear.

Epic: None
Release note (doc change): kv.transaction.write_buffering.enabled is removed from the public cluster settings to better reflect its preview status.

Release justification: docs change.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[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 

[blathers-crl]

✅ PR #162002 is compliant with backport policy

Confidence: high
Backward compatible: true
Explanation: The PR makes a change to a cluster setting but does it in a manner consistent with a disabled feature flag. Specifically, the PR's code changes to 'pkg/kv/kvclient/kvcoord/txn_interceptor_write_buffer.go' involve removing the public availability flags from the 'kv.transaction.write_buffering.enabled' and related settings. This makes these settings non-public and enforces their default state as disabled. Moreover, the PR claims to only be a documentation adjustment, aligning with a scenario where the feature-setting remains essentially unchanged but is merely hidden from public API, hence not affecting functionality or backport compatibility negatively.

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

[yuzefovich]

@yuzefovich reviewed 3 files and all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @stevendanna).

[michae2]

blathers backport release-25.2.12-rc