Refactor Server.LookupVindexCreate

[beingnoble03]

Description

This PR is based on #17092. Mainly refactors prepareCreateLookup().

Related Issue(s)

• Tracking Issue: vtctldclient/vtctld: Enhance test coverage and code refactor  #16499

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[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

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• RPC changes should be compatible with vitess-operator
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• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

Attention: Patch coverage is 83.92652% with 140 lines in your changes missing coverage. Please review.

Project coverage is 67.46%. Comparing base (de16aff) to head (d914e1c).
Report is 20 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtctl/workflow/workflows.go	80.30%	89 Missing ⚠️
go/vt/vtctl/workflow/lookup.go	88.40%	45 Missing ⚠️
go/vt/vtctl/workflow/server.go	80.64%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17242      +/-   ##
==========================================
+ Coverage   67.33%   67.46%   +0.12%     
==========================================
  Files        1569     1572       +3     
  Lines      252506   252932     +426     
==========================================
+ Hits       170021   170633     +612     
+ Misses      82485    82299     -186     

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