Fixes: #19187 - Management command for fetching UN/LOCODE data and regenerating UN_LOCODE values

[bctiemann]

Fixes: #19187

This adds a management command, refresh_un_locode.py, which fetches the latest UN/LOCODE data and formats it into the appropriate ChoiceSet tuple to assign to UN_LOCODE.

This is still a draft because:

• This PR currently only adds the management command, the UN_LOCODE values in un_locode.py have not yet been updated;
• There are still some values that are encoded strangely. The source files seem to be encoded in Windows-1252/cp1252, and that is how the script treats them; the vast majority of names imported from the Subdivisions file are displayed correctly, but some (particularly in Vietnamese and some others) appear to still be wrong. If I open the CSV files directly on my Mac all the values are interpreted and displayed correctly, so either MacOS is able to do better on-the-fly encoding detection than chardet or Python's csv module can do, or there is some yet unknown character encoding that can be used to read the files.

[jeremystretch]

I'm not sure it makes sense to implement this as a management command. As this functionality is for development purposes only and (presumably) doesn't interact with NetBox data directly, IMO it should be a standalone script.

[arthanson]

See Jeremy's comment