Update preinstalled example to make buttons actually work

[Mrtenz]

Previously the preinstalled example didn't have any logic, and since it's set up to hide the header, there was no way to get out of the dialog. I've added some basic logic now, so it has a working cancel button, and a form with a submit button.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.45%. Comparing base (8c8dafe) to head (d4dcc11).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2829   +/-   ##
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  Coverage   94.45%   94.45%           
=======================================
  Files         484      484           
  Lines       10341    10341           
  Branches     1576     1576           
=======================================
  Hits         9768     9768           
  Misses        573      573           

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