Rasgoql

Changed
- Changed default behavior of to_dbt function. Instead of always appending model details to the schema.yml file (which creates duplicate entries for existing models), rql will now check if a model entry already exists in the file and overwrite it. If the model does not exist, it will be appended.

Updated:
- Jinja rendering environment to support transform updates

Fixed
- Fixed a postgres bug

Fixed
- Fixed a bug in the `get_schema` method of SQLAlchemy DW classes where users were being asked to enter an `overwrite` param they cannot access

Changed
- Changed the `get_schema` method on all DW classes to accept a single `fqtn_or_sql` variable
- Changed the behavior of transform arguments: when a Dataset or SQLChain class is passed in as an argument to a transform, it is automatically flattened to its corresponding fqtn or CTE then consumed in the transform.

Changed
- Changed the `get_schema` method on Snowflake and BigQuery DW classes to get output columns without creating views