feat: make storage internal and not publicly accessible.

[didiergarcia]

Make analytics.storage internal so that it is not publicly accessible.

While this was out of spec with the other libraries and needed to be fixed, it seems to have been this way since v1.0.0 so we might have people in the wild relying on it.

[didiergarcia]

OK, so turns out android/ uses storage to keep track of: device id, app versions, and other things so we can't just make it internal. This will take some refactoring.

Closing this PR. Adding notes the ticket and moving it back to backlog so we tackle this again later when we have to update Storage to allow an in-memory storage option.