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]

Start in src/aws_secretsmanager_caching/cache/items.py at SecretCacheObject.__refresh, then read how SecretCacheHook receives cached_obj in the get path. Confirm the current wrapping behavior for ResourceNotFoundException and define done as preserving that exception so configuration errors are distinguishable and the hook is not invoked with None.

Written by the indexing model from the issue text.