Add pixi task to save data for QGIS, for user acceptance tests

[JoerivanEngelen]

From test plan:

Run the pixi task written below. This will export data to a UGRID NetCDF and
save it under the name <......>. Open QGIS. Click "Layers" > "Add Layer" >
"Add mesh". Insert the path <......> in the text box. This will import the mesh. Verify if the mesh is rendered in two dimensions, and not as a single line of cells. If not open an issue on GitHub.

  pixi run export-qgis

This pixi task still needs to be added.