chore: Deprecate ariaLabel in ChatBubble component

[johannes-weber]

Description

The role group was preventing the contents of the chat bubble message from being announced by aria-live when the message appeared. With that the aria-label property gets obsolete.

Follow up after merge:

• update example: remove deprecated ariaLabel property on ChatBubble components
• Unset ariaLabel values in website playground
• remove "Component-specific guidelines" for ariaLabel on https://cloudscape.design/components/chat-bubble/?tabId=usage

Related links, issue #, if available: AWSUI-60402

How has this been tested?

• verified manually

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.86%. Comparing base (8920006) to head (0c2153e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #44      +/-   ##
==========================================
- Coverage   97.87%   97.86%   -0.02%     
==========================================
  Files          30       30              
  Lines         707      701       -6     
  Branches      110      110              
==========================================
- Hits          692      686       -6     
  Misses         12       12              
  Partials        3        3              

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