Setup process requires external website

[ajparsons]

The setup process currently pulls some information directly from external websites. This means a change throws out the setup process when trying to solve a different problem.

Given we pull other datasets from github anyway, suggest separating out these scripts into a repo that uses a github action to periodically update itself. This should fail safely (cape can still set using the older version of the file), while generating errors to be addressed independenty.

[ajparsons]

One solution would be to move the website information into https://github.com/mysociety/uk_local_authority_names_and_codes/, given this changes infrequently and we reference that sheet anyway.