OpenID Connect realm is missing populate_user_metadata property

[A-Hall]

Elasticsearch version (bin/elasticsearch --version): 7.4.0

Description of the problem including expected versus actual behavior: Per the OIDC guide and this linepopulate_user_metadata is a valid setting for the OIDC Realm. However, this line in the code prevents the node from starting when the setting is configured.

[elasticmachine]

Pinging @elastic/es-security (:Security/Authentication)