Drive sqllogictest runner on directory contents rather than hard coded list

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
I want to add new tests based on the sqllogictest runner

However, doing so now requires me to edit Rust code

Describe the solution you'd like
I would like the runner to run all .sql files in a directory

Describe alternatives you've considered
Leave it as is

Additional context
I love the sqllogictest runner!