chore: Remember your theme selection in the sample app

[mattcreaser]

• PR conforms to Pull Request guidelines.

Issue #, if available:

Description of changes:
Save your theme selections across app restarts in the authenticator sample app. Also makes dynamic theme a separate option.

How did you test these changes?
Verified themes are remembered

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Ensure commit message has the appropriate scope (e.g fix(liveness): message, fix(authenticator): message, fix(all): message)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 32.59%. Comparing base (2dcec64) to head (4aae4d1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #259   +/-   ##
=======================================
  Coverage   32.59%   32.59%           
=======================================
  Files         100      100           
  Lines        4608     4608           
  Branches      583      583           
=======================================
  Hits         1502     1502           
  Misses       2950     2950           
  Partials      156      156           

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