Asset tests are failing due to savedObject field is missing from the API response GET /api/fleet/epm/packages/<package>/<version>.

Probably related to this https://github.com/elastic/kibana/pull/198434/files#diff-466e258cb2e72645d2355d6d3bdb742b38059e03eb1830ee04afb79234520d1bR673

The same data that was present in savedObject is available in the installationInfo field from that API response. This PR updates the response in order to get the Kibana and Elasticsearch assets from the installationInfo field.

Example of builds where it is failing:
https://buildkite.com/elastic/elastic-package-test-serverless/builds/210
https://buildkite.com/elastic/integrations/builds/18433

Author's Checklist

• Test a package with a local Elastic stack running the latest 9.0.0-SNAPSHOT version.
• Test packages with a Serverless project: https://buildkite.com/elastic/elastic-package-test-serverless/builds/211

How to test this

elastic-package stack down -v
elastic-package stack update -v --version 9.0.0-SNAPSHOT
elastic-package stack up -v --version 9.0.0-SNAPSHOT

cd test/packages/parallel/apache
elastic-package test -v

# test other packages if required

elastic-package stack down -v