Read CSV format text from stdin or memory

Hello,

I'm building a command line tool that can run SQL queries on text files (csv, json-line ..) . But the `CsvExec` in datafusion can only read csv text from files currently. I have checked its inner implantation the csv reader in arrow, anything impl `Read` cound be a valid input.

Should this feature ( read csv from stdin) come with datafusion ? Or I just make it into my own crate.