release-24.3: spanlatch: add cluster setting for slow latch request threshold

[angeladietz]

Backport 1/1 commits from #158472.

/cc @cockroachdb/release

---

This adds a new cluster setting
kv.concurrency.slow_latch_request_duration which configures the threshold for logging slow latch acquisitions. Previously, logging would occur after 15 seconds, but now the default is reduced to 5s.

Informs #154271
Release note: None
Epic: None
Part of: CRDB-54843

Release justification: low risk obs improvement to help debug slow latch requests

[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?

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[cockroach-teamcity]

This change is 

[blathers-crl]

✅ PR #160036 is compliant with backport policy

Confidence: high
Feature flag detected: Yes
Backward compatible: true
Explanation: The pull request meets the backport policy for CockroachDB. It adds a new cluster setting kv.concurrency.slow_latch_request_duration, which is disabled by default with a change default setting from 15 seconds to 5 seconds for slow latch acquisition logging. This cluster setting allows enabling or disabling the feature at runtime and serves as a feature flag. The PR contains a valid release justification stating it is a 'low risk obs improvement to help debug slow latch requests.' Additionally, the changes do not remove any version gates nor introduce backward compatibility issues. Both the cluster settings and the modification of existing behavior are properly handled to ensure no adverse effects on existing functionalities.

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