Add cargo purl_type to application setting

What does this MR do and why?

Add cargo as a default to package_metadata_purl_types and add cargo to existing application settings.

This will enable ingestion of cargo sboms and the sync of cargo package_metadata.

This MR second of 2:

1. Add cargo as valid type to sbom functionality and package_metadata sync: Add cargo purl_type to package_metadata sync (!155751 - merged) • Igor Frenkel • 17.1
2. Add cargo to enabled instance purl_types so that package_metadata for this can be ingested: 👈 this MR.

How to set up and validate locally

1. Run migration

   ap = ApplicationSetting.last
   ap.package_metadata_purl_types # 14 should appear here

2. Verify that column default is updated

   gdk psql
   \d application_settings -- find package_metadata_purl_types column

Related to #456283 (closed)