Clarify the usage of Auth groups with the Storage feature sets

**Is your feature request related to a problem? Please describe.**

When a developer is using Authentication groups, we need to make it clear in our documentation how these groups can be used to manage access level control for files in the Storage feature set.

**Describe the solution you'd like**

Add details in the documentation on updating the Storage resources to allow the usage of Auth groups.

**Additional context**
Here is an example where that clarification would have been helpful! https://github.com/aws-amplify/amplify-flutter/issues/1853#issuecomment-1307749732