Adding US network to station_networks.json

[MGNute]

This is a pretty minor point, but I'd like to add the NOAA CORS station network to the file station_networks.json. In general, the station names in across networks are not unique; in particular, the station name gasa exists in the US network as well as the Korea network. Granted it's only one station out of ~2700 in the US (it was the only duplicate based on my list from 2 years ago). For now I can add all the US stations to that file except gasa, but this could end up an issue if we add other networks in the future. Not a huge deal, but noted.

[tylerni7]

I think probably we should revamp the network names. I was considering just explicitly using {countrycode}_{station name} instead of just {station name} or something. This can remove the need for the station_networks.json (since we can just use the prefix), and could remove ambiguity.