[release-21.0] Fix how we generate the query serving error documentation (#17516)

[vitess-bot]

Description

This is a backport of #17516

[vitess-bot]

Review Checklist

Hello reviewers! 👋 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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• There should be a comment at the top of each new or modified test to explain what the test does.

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Backward compatibility

• Protobuf changes should be wire-compatible.
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• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.54%. Comparing base (332cfc2) to head (23dd129).
Report is 6 commits behind head on release-21.0.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-21.0   #17536      +/-   ##
================================================
+ Coverage         67.51%   67.54%   +0.03%     
================================================
  Files              1570     1570              
  Lines            251472   251483      +11     
================================================
+ Hits             169783   169874      +91     
+ Misses            81689    81609      -80     

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