feat(module:descriptions): add extra property

[wzhudev]

fix(module:descriptions): fix header DOM structure

close #5855

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
[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
[ ] No

Other information

[codecov]

Codecov Report

Merging #5859 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5859   +/-   ##
=======================================
  Coverage   90.02%   90.02%           
=======================================
  Files         463      463           
  Lines       13920    13920           
  Branches     2201     2201           
=======================================
  Hits        12531    12531           
  Misses        854      854           
  Partials      535      535           

Impacted Files	Coverage Δ
components/descriptions/descriptions.component.ts	100.00% <ø> (ø)

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