[CBBS] Extract cloud interface logic into common functions

What's the issue?
The current implementation for cloud is S3 specific (but backed by an interface). This is good, but when adding new cloud providers, we will have to duplicate the core logic (i.e. rotation/filtering) across cloud providers; this isn't ideal.

What's the fix?
The core logic should be able to work irrelevant of which cloud provider is being used (IO specifics should be handled by the clients transparently).