Add documentation example for dynamically hiding widgets

[jglev]

First, thank you very much for your work on this project! I'm grateful for the work that's gone into the project to date.

Reasons for making this change

This PR updates the "Hidden Widget" documentation to include an example for dynamically hiding / filtering aspects of large forms. This new documentation would answer rjsf-team#598. The change I've proposed does not illustrate using a search box and the component's React state, but could be expanded to.

Is this a change that you think would be useful for others in the community to have available as an example?

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 updated docs if needed
  • I've run npm run cs-format on my branch to conform my code to prettier coding style
• I'm adding a new feature
  • I've updated the playground with an example use of the feature