make pricing data more up to date

[falkben]

Currently, the pricing data are updated along with all the regular metadata about every week, per steamapp. This is because it takes that long to iterate over all the steamapps.

If we set a filter on the response data, you can request data on multiple apps at a time.

If we filtered just for pricing data, we could then request maybe even hundreds of apps at a time and be able to keep the database much more up to date (with pricing changes).

If we want historical pricing data per app, we could consider creating a new table, however we will want to be careful since pricing changes on apps may make the database much larger. We'd certainly only want to make inserts to the database on changes (not for every time we run the pricing update)

Ideally, we'd want to run the pricing update separately (on a separate cadence) from the metadata update we currently run.

There are likely some database schema updates that will be necessary in order to support that (e.g. price_updated_on, metadata_updated_on). See #40

Example request.: https://store.steampowered.com/api/appdetails/?appids=620,1172620&l=english&filters=price_overview

Returns:

{
  "620": {
    "success": true,
    "data": {
      "price_overview": {
        "currency": "USD",
        "initial": 999,
        "final": 999,
        "discount_percent": 0,
        "initial_formatted": "",
        "final_formatted": "$9.99"
      }
    }
  },
  "1172620": {
    "success": true,
    "data": {
      "price_overview": {
        "currency": "USD",
        "initial": 3999,
        "final": 3999,
        "discount_percent": 0,
        "initial_formatted": "",
        "final_formatted": "$39.99"
      }
    }
  }
}

More info here: https://wiki.teamfortress.com/wiki/User:RJackson/StorefrontAPI#appdetails