Report Air Quality -- Add optional metric flag

[rwaweber]

Using data gathered from https://waqi.info I think it could be feasible to aggregate air quality information for a given area.

Access to their API is kept behind an access token system, with access granted to non-bots.

Since this isn't technically part of the national weather service api, I think making this metric a toggle-able may be the best approach. I imagine something similar to how the node_exporter has "disabled by default" flags is sort of how I would imagine this could be tackled.

Oddly enough, recording air quality over time is how I got the idea for this project.