Implement functions for Finalizer to perform the calibration on population and structural value

Exposure-lib needs to provide the following functions for the calibration (see https://git.gfz-potsdam.de/globaldynamicexposure/collaboration/-/issues/578) to work:

• Calculate the total population and total structural value over all tiles of a country (from Asset table)
• Perform the calibration on all assets of a country