Get headers for field value for child document
head/documents/{objectTypeName}/{documentId}/children/{childDocType}/{childDocId}/fields/{fieldName}
Gets headers for a representation of a field value for a child document. If the field is configured for masking, and if the requesting user is authorized to reveal the value of the masked field, the request will succeed. If the field is configured for masking and the requesting user is not authorized to reveal the value of the masked field, the request will fail.