Add location data to proposals export and import

Is your feature request related to a problem? Please describe.

Decidim already allows the export (PR (External link) (External link)) and (re)import (link (External link) (External link)) of proposals as CSV, JSON and Excel.

However, geographical metadata is left out from both these actions. This is something that @Pops was already saying on Github (External link) (External link) a year ago regarding the export and it doesn't seem it was fixed.

Describe the solution you'd like

When exporting proposals, both the address and the coordinates (latitude, longitude) should be included.

In the JSON export, the format could be the same as the API (see example (External link) (External link)), with an address string field and and a coordinates object containing two number fields (latitude and longitude).

When exporting to a table (CSV or Excel), the columns could be named simply address, latitude and longitude.

When importing, the exact same fields should be read so it is easy to reimport an exported file.

Describe alternatives you've considered

To make it consistent with the other fields, the columns of the table files could be named address, coordinates/latitude and coordinates/longitude.

Could this issue impact on users private data?

No.

Funded by
Funding available, I've already implemented most of the import and the export doesn't seem much harder. I might need some help with the tests.