[CT-1919] Create get_column_schema_from_query macro

[MichelleArk]

get_columns_in_query retrieves a list of column names from a model's sql by running an inexpensive select * from {{ sql }} where false limit 0 query. Currently, this macro is leveraged to efficiently enforce that a model's contracted names match with what its sql would actually produce.

However, we'll need to be able to retrieve column data types in addition to column names from a model's sql in order to enforce a model contract complete with data types.

Let's create a new macro, get_column_schema_from_query with a default implementation that returns a list of Column objects with column name and type. This macro will need to rely on adapter-specific implementations to data type off the connection cursor/API. Because aapter-specific connections may return data type representations that do not match up with user-provided values, we’ll need to use dbt adapters’ type translation (aliases → standard), to match up data types with user-provided values.

@jtcohen6 has taken a very thorough first stab at validating this approach in jerco/get-column-schema-from-query