PostGIS checkout: Filter (subset) of DB needs to be enabled

[Sameme]

@vmora Currently to filter and checkout a subset of your database is only possible with the spatialite checkout. This functionality needs to be made possible on the PostGIS view checkout as well.

[gignacnic]

This functionality can be develop as it was for the SL file, as creating a temp checkout view with filter using ogr2ogr and create it in the new checkout schema.

[vmora]

@gignacnic actually it's even simpler because the postgis checkout is already a view, we only need to add a condition (id in) to the view defiinition.