Track shard session affecting change inside the transaction

[harshit-gangal]

Description

This PR adds tracking on per shard transaction on VTGate Session to know if DMLs caused any modification in the underlying database.

This will be used to restrict the participants of cross shard transactions ignoring non-modified shards from the list.
As this is part of VTGate Session, it cannot be used in same release as it could potentially break VTGate upgrade

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

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[codecov]

Codecov Report

Attention: Patch coverage is 96.29630% with 4 lines in your changes missing coverage. Please review.

Project coverage is 67.42%. Comparing base (216fd70) to head (1d465bb).
Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtgate/safe_session.go	95.45%	3 Missing ⚠️
go/vt/vtgate/scatter_conn.go	97.61%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17266      +/-   ##
==========================================
+ Coverage   67.39%   67.42%   +0.03%     
==========================================
  Files        1570     1574       +4     
  Lines      252917   253313     +396     
==========================================
+ Hits       170446   170795     +349     
- Misses      82471    82518      +47     

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[GuptaManan100]

I don't quite get why this ignoreOldSession field is required.

[harshit-gangal]

This is for reserved connection, when they are rebuild, the old session instance held should be ignored
and a new shard session should append

[GuptaManan100]

Can't we continue to use the reserveid and transaction id fields like we were using before?

[systay]

LGTM