RPC Server: support ephemeral models

[drewbanin]

Issue

Issue description

The execute and compile endpoints of the RPC server should support ephemeral models. Presently, referencing an ephemeral models fails with:

'ParsedNode' has no attribute 'extra_ctes_injected'

Reproduction

models/base/my_ephemeral_model.sql

{{ config(materialized='ephemeral') }}

select 1 as id

Query

select * from {{ ref('my_ephemeral_model') }}

Compiling/executing this query should result in:

with __dbt_cte_my_ephemeral_model as (
  select 1 as id
)

select * from __dbt_cte_my_ephemeral_model

(or similar)