docs(sbb-action-group): add button-size small

[DavideMininni-Fincons]

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the pull request tracker for a Pull Request (PR) that matches the one I want to submit, without success.

Issue

This PR Closes #2583

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

See Review Guidelines for more information what is checked during review process.

Changes

Changes in this pull request:

• add stories with button-size='s' in action-group stories

Browsers

I tested the build on the following browsers:

• Firefox Desktop
• Chrome Desktop
• Edge Desktop
• Safari Desktop
• Chrome Mobile
• Safari Mobile

Screen readers

I tested the build on the following browsers:

• JAWS Firefox Desktop
• JAWS Chrome Desktop
• NVDA Firefox Desktop
• NVDA Chrome Desktop
• VoiceOver Safari Desktop
• VoiceOver Chrome Desktop
• VoiceOver Safari Mobile
• Android Accessibility Suite Chrome Mobile

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Does this introduce a breaking change?

• Yes
• No

Other information

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (main@ddfd884). Click here to learn what that means.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2585   +/-   ##
=======================================
  Coverage        ?   93.18%           
=======================================
  Files           ?      315           
  Lines           ?    25381           
  Branches        ?     2058           
=======================================
  Hits            ?    23652           
  Misses          ?     1696           
  Partials        ?       33           

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[jeripeierSBB]

LGTM, maybe shorten stories

[jeripeierSBB]

LGTM