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

[vitess-bot[bot]]

Description

This is a backport of #16769

[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

• [ ] Apply the release notes (needs details) label if users need to know about this change.
• [ ] 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

• [ ] Is this flag really necessary?
• [ ] Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• [ ] Each item in Jobs should be named in order to mark it as required.
• [ ] If the workflow needs to be marked as required, the maintainer team must be notified.

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 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 :warning:
go/vt/wrangler/materializer.go	50.00%	4 Missing :warning:
go/vt/vtctl/workflow/server.go	50.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ 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[bot]]

This PR is being marked as stale because it has been open for 30 days with no activity. To rectify, you may do any of the following:

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If no action is taken within 7 days, this PR will be closed.