Add keyboard avoiding view examples (#30380)

Summary:
Added examples to keyboard avoiding view in RNTester for:
1. contentContainerStyle
2. enabled

## Changelog

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[General] [Added] - Add keyboard avoiding view examples

Pull Request resolved: https://github.com/facebook/react-native/pull/30380

Test Plan: ![Example](http://g.recordit.co/At5k7cF4kA.gif)

Reviewed By: PeteTheHeat

Differential Revision: D25399114

Pulled By: rickhanlonii

fbshipit-source-id: 4b893b5be02770eb582807add5f8d7dbb7941549