Enrich Vulnerabilities ES index with false positive flag data

The Vulnerabilities Elasticsearch reference class currently lacks false_positive information, preventing search and filtering by this flag.

Changes:

• Add Search::Elastic::Preloaders::Vulnerability::FalsePositive to batch-load flag data.
• Enhance proxies to include false_positive alongside existing enrichment fields.
• Update ES schema and reference class to index the field once migration completes.
• Default false_positive to false when unavailable.