Add cve column to pm_advisories

Following scale issues caused by querying through the pm_advisories identifiers field (a json list), we understand that this approach is not scalable and not reliable for our purposes of exposing CVSS values in the vulnerability details page.

The reason for the querying is to identify advisories with a specified CVE ID so we may retrieve their CVSS score.

To avoid querying through the json, we may take a denormalization approach and add a cve column directly to the pm_advisories table.

This is a follow-up to Expose CVSS, KEV and EPSS score to Vulnerabilit... (#499408 - closed).

Implementation plan

1. Add a cve column to the pm_advisories table.
2. Implement a functionality in the PMDB advisory ingestion to populate the field.
3. Either use a background migration, post-migration, or run a full re-ingestion to populate the field for all CVEs.