Consensus Health: how many medians does each bandwidth authority control?

When we change the bandwidth authorities, we want to know what impact this has on their measurements.

This matters most for:

• new bandwidth authorities, and
• changing the location of bandwidth authorities or bandwidth servers

It would help us if we knew for each relay:

• the median bandwidth authority: the bandwidth authority that made the relay's median measurement

This tells us which authority has control over the measurement. One way to implement this would be to make the median bold in each relay's bandwidth row.

It would also help us if we knew for each bandwidth authority:

• how many relays have its measurement as the median

One way to implement this is to add to the "Bandwidth scanner status" table: https://consensus-health.torproject.org/#bwauthstatus

longclaw	7845 measured	1569 median
gabelmoo	7419 measured	1484 median

It would also be helpful to have a graph of how this changes over time.