View current IP pool utilization (CRDB)

[david-crespo]

We want to be able to show IP pool utilization alongside compute, memory, and storage. Miniminally this could simply be a count of IPs allocated vs. the total number in a given pool, but ideally we would also break down ephemeral vs. floating vs. SNAT.

Note this issue does not call for tracking allocations in real time as IPs are allocated and deallocated, which would allow us to show a timeseries chart in the web console. That second stage is tracked in #5190.