vtorc: add stats to shard locks and instance discovery

[timvaillancourt]

Description

This PR adds stats to shard locks and DiscoverInstance in VTOrc

Also logic.LockShard(...) was moved to go/vt/vtorc/logic/topology_recovery.go because it's not related to tablet discovery and is only called in topology_recovery.go

Related Issue(s)

#17330

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]

Review Checklist

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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.

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• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

Attention: Patch coverage is 4.87805% with 39 lines in your changes missing coverage. Please review.

Project coverage is 67.55%. Comparing base (dd5d4c8) to head (0071555).
Report is 49 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtorc/logic/topology_recovery.go	5.71%	33 Missing ⚠️
go/vt/vtorc/logic/vtorc.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17977      +/-   ##
==========================================
- Coverage   67.56%   67.55%   -0.01%     
==========================================
  Files        1597     1597              
  Lines      259880   259897      +17     
==========================================
+ Hits       175575   175584       +9     
- Misses      84305    84313       +8     

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[GuptaManan100]

LGTM