[release-20.0] Migrate Workflow: Scope vindex names correctly when target and source keyspace have different names (#16769)

[vitess-bot]

Description

This is a backport of #16769

[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 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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• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

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]

Codecov Report

Attention: Patch coverage is 50.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 68.66%. Comparing base (b058ba2) to head (333888d).
Report is 17 commits behind head on release-20.0.

Files with missing lines	Patch %	Lines
go/vt/vtctl/workflow/materializer.go	50.00%	4 Missing ⚠️
go/vt/wrangler/materializer.go	50.00%	4 Missing ⚠️
go/vt/vtctl/workflow/server.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-20.0   #16815      +/-   ##
================================================
- Coverage         68.66%   68.66%   -0.01%     
================================================
  Files              1541     1541              
  Lines            197937   197953      +16     
================================================
  Hits             135922   135922              
- Misses            62015    62031      +16     

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[github-actions]

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