Refactor `Server.LookupVindexCreate`

[beingnoble03]

Description

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

Related Issue(s)

• 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[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 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 :warning:
go/vt/vtctl/workflow/lookup.go	88.40%	45 Missing :warning:
go/vt/vtctl/workflow/server.go	80.64%	6 Missing :warning:

Additional details and impacted files

```diff @@ 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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