Add a `vortex_metadata` table UDF to display metadata in Datafusion

Both Datafusion (in the CLI and in [dft](https://github.com/datafusion-contrib/datafusion-dft/blob/main/crates/datafusion-functions-parquet/src/lib.rs#L146)) and DuckDB expose UDFs to explore a file's metadata, which is seems very useful when trying to understand issues and performance over a large number of files.