feat: Timeline.Item support label

[shaodahong]

🤔 This is a ...

• New feature
• Bug fix
• Site / document update
• Component style update
• TypeScript definition update
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

Resolve #17966

💡 Background and solution

📝 Changelog

Language	Changelog
🇺🇸 English	Timeline.Item 支持 label
🇨🇳 Chinese	Timeline.Item support label

☑️ Self Check before Merge

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

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View rendered components/timeline/demo/label.md

[ant-design-bot]

[codecov]

Codecov Report

Merging #21560 into feature will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           feature   #21560      +/-   ##
===========================================
+ Coverage    97.84%   97.85%   +<.01%     
===========================================
  Files          304      304              
  Lines         7020     7024       +4     
  Branches      1946     1948       +2     
===========================================
+ Hits          6869     6873       +4     
  Misses         151      151

Impacted Files	Coverage Δ
components/timeline/TimelineItem.tsx	91.66% <100%> (+0.75%)	⬆️
components/timeline/Timeline.tsx	100% <100%> (ø)	⬆️

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