VReplication: Improve workflow cancel/delete

[mattlord]

Description

This work makes three key changes:

1. Remove the workflow artifacts after removing the workflow record in Workflow Delete (this is used by the cancel sub-command in all of the workflows: MoveTables/Reshard, etc). Otherwise you can see unexpected query errors in the workflow against the table between when the table is dropped and the workflow deleted.
   - This is otherwise benign, but we should still do these operations in a correct order
2. Not fail the delete/cancel if a denied tables entry is not found (we did not put those in place until you've started switching traffic)
   - If you're doing a ReverseTraffic call where the original (now frozen) workflow is deleted and another variant of it created, then this could result in the workflow being gone/deleted
   - Related to this, we now put those DeniedTables entries — a secondary safety measure, in addition to the routing rules, which prevent writes from being executed against the wrong side/keyspace which would result in data drift and potentially lost writes (if not otherwise detected with VDiff and manually corrected) — in place on the target during workflow creation rather than waiting until the first traffic switch. Previously those would only be put in place on the original workflow target after SwitchTraffic->ReverseTraffic.
   - More generally, we now do not fail the delete/cancel if the thing we went to remove is already gone or the thing we went to add is already in place
3. Now, for MoveTables workflows, we should always have DeniedTables entries on the target keyspace so I standardized the handling of those when doing traffic switches

Finally, I added a new unit test framework and tests to cover this new behavior and moved the basic VReplication endtoend test over to explicitly/statically using vtctldclient where it was previously explicitly/statically using vtctlclient (the V2 test uses vtctldclient exclusively whereas the basic test chooses the client randomly for most things so that we continue testing both until vtctlclient is removed — the things I changed are the instances where we were using a static client).

Related Issue(s)

• Fixes: Bug Report: cancelling MoveTables errors with 'cannot remove tables since one or more do not exist in the denylist' #15963
• Fixes: Bug Report: VReplication may delete the workflow on failed ReverseTraffic #14276

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

[vitess-bot]

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[rohit-nayak-ps]

Thanks! Great to see the unit test framework enhancements.