Improve US subscription state mappings (DENG-2099)

[sean-rose]

DENG-2099: Add the geo information(state for US) to the VPN subscription data

The US ZIP codes public data source I started using in #4675 turned out to be missing at least 2,656 ZIP codes (maybe because it was last updated in February 2020?), and unfortunately I haven't been able to find any other good data source for ZIP codes:

• It seems like to get all ZIP codes from USPS you have to pay them money.
• This public list from USPS is missing over 5k ZIP codes.
• In the past we've used Stripe US customer billing addresses that have both ZIP codes and states specified to fill in states elsewhere, but those are missing at least 16k ZIP codes and are generally no longer being set in Stripe going forward.

This PR instead implements an approach of using ZIP code prefixes which may be less precise in some cases, but will be more comprehensive (4,386 more US subscriptions will get their state location mapped), and hopefully won't be too much hassle to maintain.

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[sean-rose]

This was the first time I've come across Simple English Wikipedia. I cited the Simple English Wikipedia version because it was the easiest place to quickly get the data in a reasonable format, compared to the equivalent page on normal Wikipedia which has a highly formatted table that'd be much harder to copy the data from.

[sean-rose]

District X covers both NT and NU, so we can't tell which one.