fix: update Simple example so that lastName fails required field validation

[heath-freenome]

Reasons for making this change

Issue #3440 describes the required field validation for firstName and lastName not working for the simple example

• Updated the simple example to remove the ui:emptyValue for the lastName field so that required field validation works for it.
  • Also added a placeholder for firstName indicating that it will never fail validation due to ui:emptyValue

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
• I'm adding or updating code
  • I've added and/or updated tests. I've run npm run test:update to update snapshots, if needed.
  • I've updated docs if needed
  • I've updated the changelog with a description of the PR
• I'm adding a new feature
  • I've updated the playground with an example use of the feature