Atomic Transaction Startcommit api to return the commit state

[harshit-gangal]

Description

This PR adds StartCommit API state to the response from VTTablet.
This can be used by VTGate as Transaction Coordinator to take faster rollback decision.
There are 3 states:

1. Unknown - Action: VTGate leave the transaction open for the transaction resolver to resolve it later
2. Fail - Action: VTGate rollback the transaction in the RMs except in MM
3. Success - Action: VTGate proceed with next steps of Distributed Transaction Commit Flow.

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

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

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• There should be a comment at the top of each new or modified test to explain what the test does.

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Backward compatibility

• Protobuf changes should be wire-compatible.
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• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

Attention: Patch coverage is 87.36842% with 12 lines in your changes missing coverage. Please review.

Project coverage is 67.17%. Comparing base (6ad9898) to head (cc8add3).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtcombo/tablet_map.go	0.00%	3 Missing ⚠️
go/vt/vttablet/tabletserver/dt_executor.go	66.66%	3 Missing ⚠️
go/vt/vttablet/grpctabletconn/conn.go	75.00%	2 Missing ⚠️
go/vt/vttablet/sandboxconn/sandboxconn.go	93.10%	2 Missing ⚠️
go/vt/vtexplain/vtexplain_vttablet.go	0.00%	1 Missing ⚠️
go/vt/vtgate/tx_conn.go	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17116      +/-   ##
==========================================
+ Coverage   67.14%   67.17%   +0.03%     
==========================================
  Files        1571     1571              
  Lines      252093   252295     +202     
==========================================
+ Hits       169269   169484     +215     
+ Misses      82824    82811      -13     

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[GuptaManan100]

LGTM!