This PR uses a new extension point that's being added to Elasticsearch (see https://github.com/elastic/elasticsearch/pull/27603) so that the security plugin can filter the mappings fields returned by get index, get mappings, get field mappings and field capabilities API.
This effort aims at filtering information returned by API in the `indices/admin` category and field capabilities. It doesn't filter what the cluster state api returns as that is a cluster level operation.
One question is about backwards compatibility given that we would like to have this in 6.2. Shall we treat this as a bug as mappings should have been filtered before? Not sure if it's going to break existing integrations.
relates elastic/x-pack-elasticsearch#340
Original commit: elastic/x-pack-elasticsearch@d7e3fd3fa1
Luca Cavanna
lcawley