Syntax for converting file formats

[Luca]

Problem description

Currently the Polars CLI has the following syntax for converting a file from CSV to Parquet:

polars -o parquet "SELECT * FROM read_csv('data.csv')" > data.parquet

This is already helpful, however could we add syntactic sugar so that the following becomes possible:

polars -s csv -o parquet data.csv > data.parquet

(or anything similar)

this would make for a very easy syntax for running simple file conversion. And use SQL whenever we need something more advanced than a simple file conversion

[Luca]

tagging @universalmind303 for your thoughts

[Cory Grinstead]

Transferring this to https://github.com/pola-rs/polars-cli