refac: Refactor Server.GetWorkflows()

[beingnoble03]

Description

• Refactors GetWorkflows() monolithic function into utility functions in workflows.go
• Makes use of named rows instead of index based in the utility functions
• Adds tests for uncovered functions (fetchCopyStatesByShardStream, WorkflowStatus, getWorkflowCopyStates)

Related Issue(s)

• Tracking Issue: vtctldclient/vtctld: Enhance test coverage and code refactor  #16499

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

[codecov]

Codecov Report

Attention: Patch coverage is 80.56156% with 90 lines in your changes missing coverage. Please review.

Project coverage is 67.47%. Comparing base (4550640) to head (60a1ce9).
Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtctl/workflow/workflows.go	80.30%	89 Missing ⚠️
go/vt/vtctl/workflow/server.go	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17092      +/-   ##
==========================================
+ Coverage   67.15%   67.47%   +0.31%     
==========================================
  Files        1571     1570       -1     
  Lines      252250   252191      -59     
==========================================
+ Hits       169409   170159     +750     
+ Misses      82841    82032     -809     

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