feat: add metrics for atomic distributed transactions

[harshit-gangal]

Description

This PR adds metrics to distributed transaction comit flow for tracking timings and failures.

New Metrics:

• VTGate

  • CommitModeTimings - Timing metrics for commit (Single, Multi, TwoPC)
  • CommitUnresolved - Counter for failure after Prepare

• VTTablet

  • UnresolvedTransaction - Gauge to track current unresolved transactions in Metadata and Resource Manager.
  • CommitPreparedFail - Transactions that failed to commit after prepare (classified into Retryable and Non-Retryable)
  • RedoPreparedFail - Transactions that failed to re-prepare (classified into Retryable and Non-Retryable)

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 78.00000% with 11 lines in your changes missing coverage. Please review.

Project coverage is 69.34%. Comparing base (4e89152) to head (dfa8aac).
Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vttablet/tabletserver/dt_executor.go	73.33%	4 Missing ⚠️
go/vt/vttablet/tabletserver/tabletserver.go	66.66%	4 Missing ⚠️
go/vt/vttablet/tabletserver/production.go	0.00%	2 Missing ⚠️
go/vt/vttablet/tabletserver/tx_engine.go	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16939      +/-   ##
==========================================
- Coverage   69.35%   69.34%   -0.01%     
==========================================
  Files        1571     1571              
  Lines      204149   204214      +65     
==========================================
+ Hits       141583   141613      +30     
- Misses      62566    62601      +35     

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[systay]

mind adding a comment about what this is?

[harshit-gangal]

I will add on a follow up PR.