[Enh]: Include fields in `describe_entities` from metadata when not in `fields[]`.

[JerryNixon]

What?

Today fields are only included in describe_entities when the fields[] property includes them.

This enhancement includes fields (based on the role) in describe_entities from fields[] as the primary source and the database metadata as the secondary source.

This ensures every field is always included in describe_entities.

(internal reference: tribat)