Work out a policy for resolving differences between torflow and sbws

In #27135 (moved), we talk about how to deal with differences between torflow and sbws.

Here are some options:

1. Any difference between sbws and torflow is a bug in sbws that should be fixed.
2. If a sbws deployment is within X% of an existing bandwidth authority, sbws is ok. (The total consensus weights of the existing bandwidth authorities are within 50% of each other, see #25459 (moved).)
3. Let's choose an ideal bandwidth distribution for the Tor network, and modify sbws until we get that distribution.

Juga suggested that we start with policy 2, and use research to work out when to move to policy 3.