Update package metadata schema to support license deduplication

Why are we doing this work

To deduplicate the current package metadata dataset a new column is needed to store licenses without going to the join tables (pm_package_versions and pm_package_version_licenses).

In order to fully re-import the license dataset while keeping the sync positions on instances that already have package metadata, a new checkpoint needs to be created. The checkpoint has the same version_format and accesses the same urls.

Relevant links

Implementation plan

• add migration to update pm_packages
  • add jsonb column
• update model and validation with json_schema