Improve access to blob storage and document

[seabbs]

Currently this is crudely implemented using azcopy but unfortunately it has been difficult to control folder paths included. A more robust approach to this would be very helpful for downstream users. This should also be paired with new documentation.

The features this is missing which would be nice to have are:

• Flagging where estimates are available for.
• Getting latest only estimates or estimates from a date.
• Filtering to only download a specified dataset.

See R/get_estimates.R for the current implementation.

It looks like using az storage may be a solution to this as wild cards in folder paths are supported.