fix: restore focus to header when exiting tutorial

[NathanZlion]

Description

Fix Accessibility issue for focus on the tutorial panel component. When a user exits/dismisses a tutorial, focus is automatically restored to the tutorial panel header to maintain proper keyboard navigation flow.

Related links, issue AWSUI-61570

How has this been tested?

• Tested Locally
• Added integration test to check behavior and run it locally

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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[gethinwebster]

I think it would be better to use the onExitTutorial event more directly rather than observing for changes here, it should make the code a bit clearer to read and avoid needing useEffect

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.13%. Comparing base (8c37834) to head (1c03849).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4131   +/-   ##
=======================================
  Coverage   97.13%   97.13%           
=======================================
  Files         873      873           
  Lines       25562    25572   +10     
  Branches     9240     9241    +1     
=======================================
+ Hits        24830    24840   +10     
  Misses        685      685           
  Partials       47       47           

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