feat(module:select): support default value not in the option list

[vthinkxie]

close #3672 close #4000

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)
[ ] 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?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

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[codecov]

Codecov Report

Merging #4261 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4261      +/-   ##
==========================================
- Coverage   92.29%   92.28%   -0.01%     
==========================================
  Files         520      520              
  Lines       10977    10978       +1     
  Branches     1988     1988              
==========================================
  Hits        10131    10131              
  Misses        422      422              
- Partials      424      425       +1

Impacted Files	Coverage Δ
components/select/nz-option.pipe.ts	100% <100%> (ø)	⬆️
components/select/nz-option.component.ts	100% <100%> (ø)	⬆️
components/dropdown/nz-dropdown.component.ts	93.75% <0%> (-2.09%)	⬇️

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