Snowddl

- Attempted to fix directory separator issues inside `DirectoryScanneer` on Windows.

- Introduced support for both `.yml` and `.yaml` config file extensions. Previously it was only `.yaml`.
- Implemented lists as possible placeholder values. Previously only scalar values were supported.
- Changed default values for `FileFormat.format_options`, `User.session_params`, `Warehouse.warehouse_params` from `None` to `{}`. It should help to prevent errors when blueprints are created dynamically in code.
- Removed `.grep()` calls and improved performance of config directory traversing.

- Added skip for stage DIRECTORY property `DIRECTORY_NOTIFICATION_CHANNEL`. It is an informational property, should not be compared.

- Added explicit notice when `CREATE OR REPLACE TABLE` is about to drop a column from table.
- It is now possible to set `is_sandbox: false` on schema level when `is_sandbox: true` on database level.
- Fixed ENV variable name `SNOWFLAKE_ROLE`.

- Added missing conversion logic for `DatabaseBlueprint` when operating in SingleDB mode. It no longer prevents schemas from being dropped in this mode.

- Added `ICEBERG_TABLE` object type to make it available for grants and permission models.