[WIP] VReplication Merge Workflows: add heuristic to handle valid duplicate key errors caused by unique key columns.

[rohit-nayak-ps]

Description

The core functionality that this PR adds is a backoff mechanism in case of ERDupKey errors. The stream that has the error, will wait for a specific period and retry, hoping that the other stream has moved forward. (See the related issue for when the error can happen).

Todos

• Identify merge workflows, for optimization, so that we don't backoff when it is not possible for another stream to unblock it!
• During backoff if a previous commit was dropped, apply it. When two row events get merged into a single transaction because of a dropped commit, and it is required that the first one has to be applied to unblock the erroring event which is part of the backoff, we end up with a deadlock and this backoff finally times out.
• Make batching dynamic per-stream so that it can be temporarily turned off during the backoff. Same reason as the previous item.
• Test coverage

Related Issue(s)

#14296

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]

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[codecov]

Codecov Report

Attention: Patch coverage is 40.21739% with 55 lines in your changes missing coverage. Please review.

Project coverage is 68.89%. Comparing base (6d43afc) to head (71bcb7a).
Report is 105 commits behind head on main.

Files with missing lines	Patch %	Lines
.../vt/vttablet/tabletmanager/vreplication/vplayer.go	33.33%	50 Missing ⚠️
...t/vttablet/tabletmanager/vreplication/vdbclient.go	54.54%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17074      +/-   ##
==========================================
- Coverage   69.51%   68.89%   -0.62%     
==========================================
  Files        1569     1572       +3     
  Lines      202529   263390   +60861     
==========================================
+ Hits       140784   181463   +40679     
- Misses      61745    81927   +20182     

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