ENH: Store time data when saving geoJSON

# Description
`geocsv2geojson()` should incorporate time information from the geoCSV into the geoJSON file. (Could make this optional.) Not currently supported by OpenSpace but now on the feature list (see https://github.com/OpenSpace/OpenSpace/issues/3701).

## Potential impact
If support for this is added into OpenSpace, it could simplify workflows, since you can drag-and-drop geoJSONs.