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

[mike-weinberg]

dbt-external-tables/macros/plugins/snowflake/snowpipe/get_copy_sql.sql

Line 32 in 4d26c38

file_format = {{external.file_format}}

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)