fix(module:config): add itemsize config for tree select table (#8347)

[EnochGao]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[X] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[X] Documentation content changes
[X] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

The gap at the bottom of the switch theme drop-down box is too large

Issue Number: #8347

What is the new behavior?

Normal clearance

Does this PR introduce a breaking change?

[ ] Yes
[X] No

Other information

none

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6024bcc) 91.74% compared to head (c9e94ca) 91.75%.
Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8361      +/-   ##
==========================================
+ Coverage   91.74%   91.75%   +0.01%     
==========================================
  Files         520      520              
  Lines       18019    18019              
  Branches     2838     2838              
==========================================
+ Hits        16531    16534       +3     
+ Misses       1185     1183       -2     
+ Partials      303      302       -1     

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[Nicoss54]

@EnochGao thanks for your PR! Great works, it will take me some time to review all the change

But again thanks for your work