koord-descheduler: fix maxMigratingGlobally arg json tag

[songtao98]

Ⅰ. Describe what this PR does

This PR add maxMigratingGlobally json tag to enable configuration of this arg.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

V. Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in make test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.85%. Comparing base (6d7b92f) to head (3209172).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2144      +/-   ##
==========================================
- Coverage   67.85%   67.85%   -0.01%     
==========================================
  Files         441      441              
  Lines       41720    41720              
==========================================
- Hits        28309    28308       -1     
  Misses      10971    10971              
- Partials     2440     2441       +1     

Flag	Coverage Δ
unittests	67.85% <ø> (-0.01%)	⬇️

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[hormes]

/lgtm
/approve

[koordinator-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hormes

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• pkg/descheduler/OWNERS [hormes]

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