feat(module:timeline): allow custom color

[ParsaArvanehPA]

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?

Currently timeline component only supports a fixed amount of colors. In ant design these set of colors are available but it is also possible to use custom colors.

What is the new behavior?

Now supports custom colors

Does this PR introduce a breaking change?

[ ] Yes
[✔] No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (74c4707) 91.73% compared to head (dfac933) 91.73%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8335   +/-   ##
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  Coverage   91.73%   91.73%           
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  Files         520      520           
  Lines       18010    18010           
  Branches     2838     2838           
=======================================
  Hits        16521    16521           
  Misses       1186     1186           
  Partials      303      303           

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[HyperLife1119]

LGTM