Add internal events for package metadata sync paths

What does this MR do and why?

Implements the observability events specified in #600562 (closed).

Three events, one per data_type (advisories / licenses / cve_enrichment). A single track_sync_path(property) helper in Gcp resolves the event name from sync_config.data_type and emits once per data_after call. label carries purl_type; property carries the path key. cve_enrichment omits label since its purl_type is always nil.

References

• Resolves #600562 (closed)
• Pattern reference (additional_properties + spec matcher): !163935 (merged)