Diagnostics page for Adaptive decisions

It can be somewhat hard to determine when / why the scheduler decides to scale the cluster under adaptive mode. Ideally a dashboard page could shed some light here.

We currently have `/json/counts.json` which provides `desired_workers`. I think that's it.

I think there are two main pieces of information to convey:

1. Stock: The current state of things including current CPU load, current CPU capacity, and the current desired CPU capacity. Likewise for memory
2. Flow: The history of decisions on when to scale up / down the cluster (ideally with information on why those decisions were made (the state at that time)

Here's a rough sketch for number 1.


cc @rsignell-usgs, @jsignell for adaptive things, and @jacobtomlinson for dashboard design things.