Add utils to automatically obtain S3 paths following the new naming convention.

[piconti]

We are in the process of identifying and finalizing naming conventions for, among other things, S3 paths.

It would be helpful and practical to implement some helper function(s) that allow to reconstruct such paths easily, relying both on the predefined conventions and the atcual contents of S3.

The action points for this are:

• Write one or several functions to get, create or complete S3 paths given the components and S3 contents.
• Write tests
• Document them

[simon-clematide]

Just saw this issue:-) my commit #90f00d01840e8f49d1958437bc36654510df84f3 solves the parsing part (once we agree on a grammar).