Refactor ItemSetService(updateSet Item) and ConfigChangeContentBuilder a little bit

[mghio]

What's the purpose of this PR

Refactor ItemSetService(updateSet Item) and ConfigChangeContentBuilder a little bit.

Brief changelog

Refactor ItemSetService(updateSet Item) and ConfigChangeContentBuilder a little bit.

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• Update the CHANGES log.

[codecov-commenter]

Codecov Report

Merging #4515 (186db81) into master (93e557e) will decrease coverage by 0.01%.
The diff coverage is 12.19%.

@@             Coverage Diff              @@
##             master    #4515      +/-   ##
============================================
- Coverage     53.47%   53.45%   -0.02%     
  Complexity     2705     2705              
============================================
  Files           491      491              
  Lines         15395    15399       +4     
  Branches       1599     1596       -3     
============================================
  Hits           8232     8232              
- Misses         6603     6607       +4     
  Partials        560      560              

Impacted Files	Coverage Δ
...apollo/adminservice/controller/ItemController.java	7.29% <0.00%> (+0.14%)	⬆️
...p/framework/apollo/biz/service/ItemSetService.java	8.95% <0.00%> (-0.89%)	⬇️
...k/apollo/biz/utils/ConfigChangeContentBuilder.java	100.00% <100.00%> (ø)

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[nobodyiam]

LGTM