Add strokeLinecap attribute to progress component

[blatinier]

Description:

Allow to control strokeLinecap of progress bar (square or round). round stays the default.

PR Checklist:

• Make sure that you propose PR to right branch: bugfix for master, feature for latest active branch feature-x.x.
• Make sure that you follow antd's code convention.
• Run npm run lint and fix those errors before submitting in order to keep consistent code style.
• Rebase before creating a PR to keep commit history clear.
• Add some descriptions and refer relative issues for you PR.

Extra checklist NewFeature:

• Update API docs for the component.
• Update/Add demo to demonstrate new feature.
• Update TypeScript definition for the component.
• Add unit tests for the feature.

[blatinier]

I did not added unit tests for it since it really just CSS stuff. I regenerated jest snapshots to pass though.

Tell me if new tests are needed.

[ant-design-bot]

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[codecov]

Codecov Report

Merging #11547 into feature-3.8.0 will increase coverage by 0.02%.
The diff coverage is 100%.

@@                Coverage Diff                @@
##           feature-3.8.0   #11547      +/-   ##
=================================================
+ Coverage          91.92%   91.95%   +0.02%     
=================================================
  Files                199      199              
  Lines               5091     5106      +15     
  Branches            1427     1436       +9     
=================================================
+ Hits                4680     4695      +15     
  Misses               407      407              
  Partials               4        4

Impacted Files	Coverage Δ
components/progress/progress.tsx	97.91% <100%> (+0.09%)	⬆️
components/timeline/Timeline.tsx	100% <0%> (ø)	⬆️

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