Add ISO3 and M49 codes in data table downloaded as CSV via the interface & remove geoentity_id

[antobenve]

The CSV that is downloaded using the interface contains the region name and the id of the country/region (Region Name | Region ID).

As this file is accessible by users who do not necessarily want to transform tables, it is best to provide a ready to use file with all the needed columns and without technical ones.

Pascal has raised the need to have the iso3 code in the table.
We suggest to do that and to also include the m49 code (useful for the entities without iso3) and to remove the geoentity_id.

This can be done in 2 ways:

1. Website level by preparing the CSV using the results from the API calls indicatorsValues and geoEntitiesMetadata which need to be joined using geoentity_id (be careful with language choise as the values are available in multiple languages).
2. Modifying the API route indicatorsValues

Option 1 is preferred in order to keep the API routes as clean as possible,