release-24.3.20-rc: kvserver: invoke callback when SetMaxSize drops replicas

[wenyihu6]

Backport 1/1 commits from #153008.

/cc @cockroachdb/release

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Epic: none
Release note: none

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kvserver: invoke callback when dropping replicas in bq.SetMaxSize

Previously, when SetMaxSize shrank the queue, replicas were dropped from the
priority queue without invoking their callbacks. This commit ensures callbacks
are properly invoked when SetMaxSize drops replicas. Replicas removed via
removeFromReplicaSetLocked (such as when a replica is destroyed) still don’t
always have their callbacks invoked. While the natural place to invoke the
callback would be at removeFromReplicaSetLocked, invoking callbacks while
holding a lock risks blocking for too long. (We are doing this already for
addInternal though.) This PR focuses specifically on handling the SetMaxSize
case since this PR is intended to be backported. We can follow up with a more
complex but more principled approach on master if needed in the future.

Release justification: low risk fix guarded behind cluster setting

[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.

[cockroach-teamcity]

This change is 

[blathers-crl]

✅ PR #153179 is compliant with backport policy

Confidence: high
Feature flag detected: Yes
Backward compatible: true
Explanation: The PR is compliant with the CockroachDB backport policy. Firstly, the PR body includes a 'Release justification: low risk fix guarded behind cluster setting' line, which provides a valid reason for the backport, exempting it from the standard policy requirements of needing to fix a critical bug or being gated behind a feature flag. Secondly, although the primary change affects production code, it is described as a low-risk fix and is explicitly mentioned to be guarded by a cluster setting. This suggest compliance with the feature flag requirement as new cluster settings controlling behavior are treated as a form of feature flag gating. Additionally, the PR does not indicate any back-breaking changes or the removal of a version gate, supporting backward compatibility.

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