Implement --test-threads CLI argument for sqllogictest runner

[alamb]

Another thing we could do (as a follow on PR) is to actually thread this through to the runner:

https://github.com/apache/datafusion/blob/eeee6b00a0a0cf1bb449631b57535c06bbf99583/datafusion/sqllogictest/bin/sqllogictests.rs#L197-L196

Originally posted by @alamb in #16694 (comment)

[alamb]

Dupe of #16721