[release-20.0-rc] VReplication: Improve workflow cancel/delete (#15977)

[vitess-bot]

Description

This is a backport of #15977

[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

• 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]

Codecov Report

Attention: Patch coverage is 45.05929% with 139 lines in your changes missing coverage. Please review.

Project coverage is 68.50%. Comparing base (965da11) to head (bec896f).

Files	Patch %	Lines
go/vt/vtctl/workflow/switcher_dry_run.go	22.42%	83 Missing ⚠️
go/vt/vtctl/workflow/traffic_switcher.go	57.35%	29 Missing ⚠️
go/vt/vtctl/workflow/server.go	61.42%	27 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##           release-20.0-rc   #16130      +/-   ##
===================================================
+ Coverage            68.24%   68.50%   +0.26%     
===================================================
  Files                 1541     1541              
  Lines               197330   197468     +138     
===================================================
+ Hits                134665   135282     +617     
+ Misses               62665    62186     -479     

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