Snowflake loader: Specify file format in the load statement

[istreeter]

Currently we expect the user to configure their Snowflake stage to be associated with a file format. Here is where it is done in the open source terraform setup.

If we put the format options directly into the COPY INTO statement then it doesn't need to be pre-configured. It is one less thing for the user to set up manually.

Also this would allow the loader to dynamically switch between loading JSON and loading PARQUET without a configuration change in Snowflake.