feat(module:steps): support for clickable steps

[hsuanxyz]

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?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[netlify]

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[codecov]

Codecov Report

Merging #3934 into master will decrease coverage by <.01%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##           master    #3934      +/-   ##
==========================================
- Coverage   95.24%   95.23%   -0.01%     
==========================================
  Files         726      727       +1     
  Lines       14672    14693      +21     
  Branches     1910     1913       +3     
==========================================
+ Hits        13974    13993      +19     
- Misses        260      261       +1     
- Partials      438      439       +1

Impacted Files	Coverage Δ
components/steps/nz-step.component.ts	97.72% <100%> (+0.5%)	⬆️
components/steps/demo/clickable.ts	83.33% <83.33%> (ø)
components/steps/nz-steps.component.ts	96.77% <92.3%> (-1.41%)	⬇️

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[wzhudev]

lgtm.

我觉得可以写个测试提升下覆盖率？@hsuanxyz