Add support for GROUPING SETS syntax in SQL planner #2469

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Issue #2378 adds support for ROLLUP and CUBE grouping sets. This is a follow on issue to also support GROUPING SETS, which may require changes to sqlparser-rs and also may require changes to the optimization rules to support Vec<Vec<Expr>>. See optimizer/utils.rs to see where this is not currently supported.

Describe the solution you'd like
Support GROUP BY foo, GROUPING SETS (a (b, c), (c, d, e))

Describe alternatives you've considered
None

Additional context
None