Use real package metadata in script service

[adrien-piquerez-da]

This PR is a follow-up of #21351, to fix the bug described in https://github.com/digital-asset/daml/issues/21324#issuecomment-2959739048.

In the script service we used to create a dummy package metadata for the self package. This causes the queryInterface to fail resolving the interface view of an upgraded template in the self package. To fix it, the daml assistant reads the real package metadata from the daml.yaml and sends it to the script service through the UpdatePackages request.