Update documentation to state that custom security policy is not taken in account with passthrough

Elasticsearch repository query takes in account ACL security and security policy that are expressible in NXQL.

The API passthrough query takes in account only the ACL security.

The doc should be updated to state on the security policy:

• https://doc.nuxeo.com/nxdoc/security-policy-service/
• https://doc.nuxeo.com/nxdoc/elasticsearch-indexing-logic/
• https://doc.nuxeo.com/nxdoc/elasticsearch-passthrough/

Some warning must be added when security policy exists and passthrough is available.