Automatic ephemeral base models

[dbrtly]

Add "identifier" config for columns in source schema.

`
sources:

• name: my_schema
  schema: actual_schema
  tables:
  • name: my_table
    identifier: actual_table
    columns:
    • name: my_col_alias
      identifier: my_column
      data_type: bigint

`

`--sql
with

{{ base("my_schema", "my_table"}},

agg as (
select sum(my_col_alias)
from my_schema__my_table
)

select * from agg

`

To:
`
With

my_schema__my_table as (
select
cast(my_column as bigint)
as my_col_alias
from actual_schema.actual_table
),

agg as (
select sum(my_col_alias) as total_whatever
from my_schema__my_table
)

select * from agg

`