file format is required in snowpipe config but isn't actually required by snowflake

[mike-weinberg]

https://github.com/dbt-labs/dbt-external-tables/blob/4d26c38c81ac7c39e9ed8f50792b43de769e88cb/macros/plugins/snowflake/snowpipe/get_copy_sql.sql#L32

it seems to me that this line could be optional, bc stages can store file formats and the file_format parameter is optional in COPY INTO (per reference docs)