Add in config to avoid AST in some join cases

[revans2]

This is intended to be a test to see if it will improve the performance in some cases so we can possibly come up with a heuristic in the future.

[revans2]

build

[jlowe]

Would it make sense to have RapidsMeta have the ability for expressions to be disabled for AST individually if spark.rapids.sql.expression.ast.classname is false? We probably still want an overall AST join enable as implemented here.

[revans2]

Would it make sense to have RapidsMeta have the ability for expressions to be disabled for AST individually if spark.rapids.sql.expression.ast.classname is false? We probably still want an overall AST join enable as implemented here.

Possibly. I'm not sure that we ever want to actually merge this in. It is here as a tool for now to see if a specific query would get faster or slower with it.