fix(module:modal): add nzOkDanger to avoid old button style

[yangjunhan]

close #6111

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?

[x] 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: #6111

What is the new behavior?

Add nzOkDanger and danger in nzFooter APIs to avoid using old danger button style.

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 #6157 (a47244f) into master (47065f6) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #6157      +/-   ##
==========================================
+ Coverage   89.81%   89.85%   +0.03%     
==========================================
  Files         468      468              
  Lines       14255    14259       +4     
  Branches     2241     2242       +1     
==========================================
+ Hits        12803    12812       +9     
+ Misses        896      891       -5     
  Partials      556      556              

Impacted Files	Coverage Δ
components/modal/modal-footer.component.ts	100.00% <ø> (ø)
components/modal/utils.ts	100.00% <ø> (ø)
components/button/button.component.ts	100.00% <100.00%> (ø)
components/modal/modal-types.ts	100.00% <100.00%> (ø)
components/modal/modal.component.ts	92.85% <100.00%> (+0.08%)	⬆️
components/time-picker/time-holder.ts	94.73% <0.00%> (-1.06%)	⬇️
components/tabs/tab-nav-bar.component.ts	82.33% <0.00%> (+0.70%)	⬆️
components/table/src/table-data.service.ts	84.61% <0.00%> (+6.15%)	⬆️

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[hsuanxyz]

LGTM