refactor: move business logic into separate file

This MR moves business logic in a separate file.

That way, the index begins with the start making easier to follow.

index.js -> start()
- /core -> business logic from "grdf tech"
- /requests -> requests from each grdf, bo, cozy 

📒 the getData methods are still in index.js but I didn't moved them to keep git history and because the new konnector changes the consent section, not getting the data