Refactor the ResourceRepository related code

[tomeresk]

The ResourceRepository interface currently keeps a lot of logic in the respective implementations of each repository (S3, FS etc.). We should refactor this to ideally have a simple abstraction layer over each repository that exposes the basic functions of working with it (get file, update file, list files etc.), and move the other logic currently in there to new abstractions (for example resource group manager, policy manager etc.).

More info and some of the discussion that prompted this issue can be found in the comments of this PR