[CT-2214] [Redshift] Use new ColumnLevelConstraint structure in redshift__get_columns_spec_ddl

[MichelleArk]

Core issue: dbt-labs/dbt-core#7066

Refactor redshift__get_columns_spec_ddl to use the new constraints data structure in favour of the existing constraints and constraints_check. Adapter specific tests should not need to change the existing expected_sql fixture is still the expected result!

Currently, redshift__get_columns_spec_ddl iterates over the user-provided columns and renders the constraint for each column constraint.

• It does some special handling of primary_key and not_null constraints: https://github.com/dbt-labs/dbt-redshift/blob/main/dbt/include/redshift/macros/utils/get_columns_spec_ddl.sql#L13-L16, which we can infer from the type attribute of the new constraints data structure.
• It does not render any check constraints because those are passed obtained col['constraints_check']. We should maintain this behaviour - constraints with type: check should not be rendered in the column spec ddl.