Create bandwidth authority specification
We have:
- https://research.torproject.org/techreports/torflow-2009-08-07.pdf
- https://gitlab.torproject.org/tpo/network-health/torflow/-/blob/main/NetworkScanners/BwAuthority/README.spec.txt
- https://gitlab.torproject.org/tpo/network-health/torflow/-/blob/main/NetworkScanners/BwAuthority/README.BwAuthorities
- https://gitlab.torproject.org/tpo/network-health/torflow/-/blob/main/README
- https://gitlab.torproject.org/tpo/core/torspec/-/blob/main/bandwidth-file-spec.txt
We should create a single "bandwidth authority spec" including data from those documents and the current implementations.