Support GDAL DEM file URI's

## Desired behavior

Allow SDFormat to load a DEM that uses the [GDAL virtual filesystem format](https://gdal.org/user/virtual_file_systems.html).

## Alternatives considered

* Skip SDF, write a custom plugin

## Implementation suggestion

```xml

false
gdal:://vsizip/vsicurl/https://terrain.ardupilot.org/SRTM1/ap_srtm1.zip/ap_srtm1.vrt

```

## Additional context

* Relates to https://github.com/gazebosim/gz-common/issues/596