Add savepoint support to atomic distributed transaction

[harshit-gangal]

Description

This PR adds support for savepoints usage in atomic distributed transaction commit by storing the savepoints in the transaction query log and then reapplying them on a recovery.

Related Issue(s)

• RFC: Atomic Distributed Transactions #16245

Checklist

• 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]

Review Checklist

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[codecov]

Codecov Report

Attention: Patch coverage is 76.29630% with 32 lines in your changes missing coverage. Please review.

Project coverage is 69.42%. Comparing base (056afc9) to head (bc836c4).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vttablet/tabletserver/tabletserver.go	64.28%	20 Missing ⚠️
go/vt/vttablet/tabletserver/planbuilder/plan.go	66.66%	5 Missing ⚠️
go/vt/vttablet/tabletserver/query_executor.go	85.71%	4 Missing ⚠️
go/vt/vttablet/tabletserver/tx/api.go	85.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16863      +/-   ##
==========================================
- Coverage   69.45%   69.42%   -0.04%     
==========================================
  Files        1570     1570              
  Lines      203631   203921     +290     
==========================================
+ Hits       141441   141563     +122     
- Misses      62190    62358     +168     

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[systay]

maybe add some comments? the type is not self evident, imho

[systay]

apart from some nitpicks, LGTM

[GuptaManan100]

This is great!