Create `ids_list_geographies()` function

[christophscheuch]

This issue includes:

• [ ] Creation of exported ids_list_geographies() function that loads pre-processed system data (see https://r-pkgs.org/data.html#sec-data-sysdata). The idea is that the geographies are not automatically exported to the users, but need to be called explicitly via ids_list_geographies().
• [ ] Creation of a script to download, process and store the geographies as system data (see https://r-pkgs.org/data.html#sec-data-data-raw).
• [ ] Get additional geography variables (e.g. capital city) from WDI API. For now, copy relevant code from https://github.com/tidy-intelligence/r-wbwdi/blob/main/R/list_supported_countries.R. Once wbwdi is on CRAN, we could use it as a suggested import in the data generation script.

In a later issue, we'll introduce standardized names: https://github.com/Teal-Insights/r-wbids/issues/18

Some notes (Teal checked, Christoph verified):

• country_id from World Bank API is the same as iso3c from countrycode. We decided to not use this package though to avoid license issues. We'll wait for the new micropackage.
• Any place there isn't a standardized country name is an aggregate (I checked). WDI API also provides information about country vs aggregate through region.
• For non-countries, we can use the aggregate name provided by World Bank API