Add shim to correct test seed data types in Snowflake

[craigrmccown]

Problem

The Snowflake schema uses the variant data type for the JSON columns event_properties and source_properties. However, dbt interprets these columns as varchar, and explicitly setting the column data type in the seed configuration results in an error.

Changes

• Provide a variable to override the table name and set it explicitly in the integration_tests package so that all models target the same identifier.
• Add a shim model that is only deployed when target.type == 'snowflake'. The shim uses parse_json to convert JSON columns to variant.
• Alias the fullstory_events_integration_tests to fullstory_events_integration_tests_raw when target.type == 'snowflake'

The result is that, in Snowflake, all views are built on top of the shim view instead of the physical seed table. Other target types are unaffected.

[camphillips22]

LGTM!