Added section on Configuring S3 Storage and Multi-Hop Transfers in Rucio

[alessio94]

Added section on Configuring S3 Storage and Multi-Hop Transfers in Rucio - developed by Ievgen Sliusar and me as part of my ATLAS Qualification Task. Link to CERNBox for original files.

[voetberg]

This is super useful, thank you for the contribution. To re-iterate what was said in the dev meeting on paper, linking to cernbox is not a very sustainable solution. I think the files can just be linked s.t. files are given as

[Your File Name Here](link/to/file.sh) 

https://docusaurus.io/docs/static-assets#in-markdown

Though, this method does automatically download the file when the user clicks them, the .sh could be rather nefarious looking. I suppose they can be uploaded as .txt files which are a little less scary, but this needs some thought.

I think making a folder in this repo called something like "_resources" that is hidden from the index would be a decent place to upload them, and a place that others can contribute to

[rdimaio]

No need to link to this, we're already on the documentation website