[FEATURE]: Create workflow to check for new UN geodata

[camdecoster]

Description

Add a GHA workflow to check for new UN geodata every month.

Why should this feature be added?

There's no check right now and it would be helpful to be notified if a new version is available.

Notes

• The UN geodata portal uses the ArcGIS API to share/query items
• The query to use is this:
  https://geoportal.un.org/arcgis/sharing/rest/search?f=json&q=(type:"geojson") AND (title:"*geodata*")&sortField=created&sortOrder=desc
• It returns a JSON list of matches