MoveTables: do not set session foreign_key_checks, if target has it turned off globally

[rohit-nayak-ps]

Description

When we implemented atomic copy when we started supporting foreign keys, we also started using the RowEvent flags attribute to set the session's foreign_key_checks variable depending on the value in the binlog event.

However in certain situations (for example: #16296) this could cause reverse workflows to fail and cannot be recovered. This PR adds logic so that vplayer will no longer set foreign_key_checks at the session level if it is turned off in the global scope.

Related Issue(s)

https://github.com/vitessio/vitess/issues/16296

Checklist

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[vitess-bot[bot]]

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[mattlord]

Makes sense IMO, for precisely the same reasons laid out here (mysqldump also disables FK checks): https://github.com/vitessio/vitess/pull/9505

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 77.77778% with 4 lines in your changes missing coverage. Please review.

Project coverage is 68.70%. Comparing base (bb76046) to head (6ac6bad). Report is 91 commits behind head on main.

Files	Patch %	Lines
.../vt/vttablet/tabletmanager/vreplication/vplayer.go	76.47%	4 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16297      +/-   ##
==========================================
- Coverage   68.71%   68.70%   -0.01%     
==========================================
  Files        1544     1544              
  Lines      198011   198028      +17     
==========================================
- Hits       136064   136057       -7     
- Misses      61947    61971      +24     

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[rohit-nayak-ps]

I feel like the problem is with the schema inconsistency, rather the specific FK checks settings. I don't have a use case, but I have the feeling that this fix will break some other scenario.

We are going to go ahead with reviewing this on its own, but we may decide to close it without merging based on other discussions we are initiating, to see if Vitess should expect a different approach by the users, for the edge-cases this PR is aiming to solve. Added do not merge for now.

[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.

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This PR was closed because it has been stale for 7 days with no activity.