Add \i command to datafusion-cli

[matthewmturner]

Taking inspiration frompsql , it implements a \i command (not a command line argument) for this usecase. It includes a file:

https://www.postgresql.org/docs/13/app-psql.html

\i or \include filename
Reads input from the file filename and executes it as though it had been typed on the keyboard.

If filename is - (hyphen), then standard input is read until an EOF indication or \q meta-command. This can be used to intersperse interactive input with input from files. Note that Readline behavior will be used only if it is active at the outermost level.

It appears that mysql has a similar command source or \. that does the same thing

https://dev.mysql.com/doc/refman/8.0/en/mysql-batch-commands.html

Thus I would recommend implementing a \i command (and possibly also a source command)

Originally posted by @alamb in #1875 (comment)