[release-23.0] Add ZooKeeper connection metrics to zk2topo (#19757)

[vitess-bot]

Description

This is a backport of #19757

[vitess-bot]

Hello @MargaretMorehead, there are conflicts in this backport.

Please address them in order to merge this Pull Request. You can execute the snippet below to reset your branch and resolve the conflict manually.

Make sure you replace origin by the name of the vitessio/vitess remote

git fetch --all
gh pr checkout 19792
git reset --hard origin/release-23.0
git cherry-pick -m 1 8edc85bdba59c1d3875546ffaeac73bacfe9655f

[Copilot]

Pull request overview

Backport that adds ZooKeeper connection observability metrics to the zk2topo connection wrapper to help debug ZooKeeper connectivity/concurrency issues.

Changes:

• Adds three new exported stats variables: lock/semaphore acquisition latency, retry attempts, and connection state transitions.
• Instruments withRetry to record semaphore wait time and retry count.
• Instruments session event handling to count ZooKeeper connection state transitions.

[promptless]

Promptless prepared a documentation update related to this change.

Triggered by this PR

Added documentation for the three new ZooKeeper connection metrics (ZkLockAcquisition, ZkConnAcquisitionRetry, ZkConnState) to the v23.0 topology service reference docs, matching the existing v24.0 documentation that was created for the original PR #19757.

Review at https://app.gopromptless.ai/suggestions/296beb0a-ffd9-4ee7-8f33-b65b03bc52ad