Don't wrap ResourceNotFoundException

If the secret is not on AWS Secrets Manager the client will throw a `ResourceNotFoundException` that will be wrapped in [`SecretCacheObject.__refresh`](https://github.com/aws/aws-secretsmanager-caching-python/blob/8b3ed311982096d6cb6a99ab33299ade3c9811b3/src/aws_secretsmanager_caching/cache/items.py#L97)

I think to **wrap `ResourceNotFoundException` is not good practice**: because after the client application has no way to understand that something is wrong in the configuration of Aws SM, and if you have a hook it will be triggered anyway even if an exception occurred and the value is None.
[the implementation of `SecretCacheHook` will receive `cached_obj = None` in the get method]

src/aws_secretsmanager_caching/cache/items.py の SecretCacheObject.__refresh から始め、次に get パスで SecretCacheHook が cached_obj を受け取る仕組みを確認します。ResourceNotFoundException の現在の wrapping 動作を確認し、設定エラーを区別でき、hook が None で呼び出されないように、その例外を保持することを完了条件とします。

索引モデルが issue の本文から書いたものです。