[release-20.0] Close zookeeper topo connection on disconnect (#17136)

[vitess-bot[bot]]

Description

This is a backport of #17136

[vitess-bot[bot]]

Review Checklist

Hello reviewers! :wave: Please follow this checklist when reviewing this Pull Request.

General

• [ ] Ensure that the Pull Request has a descriptive title.
• [ ] Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• [ ] Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

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• [ ] New features should be documented.
• [ ] There should be some code comments as to why things are implemented the way they are.
• [ ] There should be a comment at the top of each new or modified test to explain what the test does.

New flags

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If a workflow is added or modified:

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Backward compatibility

• [ ] Protobuf changes should be wire-compatible.
• [ ] Changes to _vt tables and RPCs need to be backward compatible.
• [ ] RPC changes should be compatible with vitess-operator
• [ ] If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• [ ] vtctl command output order should be stable and awk-able.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 66.42%. Comparing base (3444a1d) to head (7fee093). Report is 1 commits behind head on release-20.0.

Files with missing lines	Patch %	Lines
go/vt/topo/zk2topo/zk_conn.go	50.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release-20.0 #17192 +/- ## ============================================= Coverage 66.41% 66.42% ============================================= Files 1541 1541 Lines 243990 243986 -4 ============================================= + Hits 162055 162072 +17 + Misses 81935 81914 -21 ```

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