Sync false positive field with Vulnerability ES index

Description

Integrate ES Bookkeeping into the GitLab application so that updates to the false_positive flag in Vulnerabilities::Flag remain in sync with Elasticsearch (ES).

Implementation plan

• Update UpdateAiDetectionService to handle ES bookkeeping when creating or updating Vulnerabilities::Flag records.

Note: Later, when a Vulnerabilities::Flag false positive flag is removed, we will need to ensure the ES document for the associated vulnerability is updated accordingly to reflect the change, this is related to Add ability to remove False Positive flag from ... (#578903 - closed).