feat(module:i18n): add km_KH

[SamnangNhum]

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

What is the current behavior?

No km_KH i18n

What is the new behavior?

Add km_KH i18n

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

Merging #7220 (ed22d8d) into master (e541761) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7220      +/-   ##
==========================================
- Coverage   91.72%   91.71%   -0.02%     
==========================================
  Files         486      486              
  Lines       15950    15950              
  Branches     2591     2591              
==========================================
- Hits        14630    14628       -2     
- Misses       1010     1011       +1     
- Partials      310      311       +1     

Impacted Files	Coverage Δ
components/tabs/tab-nav-bar.component.ts	87.23% <0.00%> (-0.71%)	⬇️

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[wenqi73]

@SamnangNhum Could you help to update docs/i18n.zh-CN.md and docs/i18n.en-US.md?

[SamnangNhum]

@SamnangNhum Could you help to update docs/i18n.zh-CN.md and docs/i18n.en-US.md?

@wenqi73 I have already updated docs please checked thanks

[wenqi73]

@SamnangNhum Thanks!

[simplejason]

@SamnangNhum Can you rebase with master to resolve these conflicts? After that, @wenqi73 please recheck this PR :)