Rename Identifiers to Entities and update object keys to new spec

[QMalcolm]

In the new world of dbt-core x MetricFlow Identifiers are becoming Entities. Additionally some of the properties of the object are changing. The resulting object should have the following properties

Property Name	Type	Description
name	str	Name of the entity
type	enum	Type of the entity
description	str	Description of the entity
role	str	Role of the entity
entities	List[str]	List of composite sub-entities
expr	str	Expression of the entity

The above properties are were pulled from dbt-labs/dbt-core#7456

[callum-mcdata]

We will be removing the entities property, as we decided that we can push that logic down to the underlying dbt model. @WilliamDee I think you mentioned you didn't want that to be part of the great renaming so flagging it here