SQL: Support "subtotalsSpec"

[nrwiersma]

Description

subtotalsSpec which is closest to GROUPING SET makes it far more efficient to create multiple groups that without it, would need to be done in multiple queries.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[vogievetsky]

I think this is still relevant.

[stale]

This issue is no longer marked as stale.

[stale]

This issue has been marked as stale due to 280 days of inactivity. It will be closed in 4 weeks if no further activity occurs. If this issue is still relevant, please simply write any comment. Even if closed, you can still revive the issue at any time or discuss it on the dev@druid.apache.org list. Thank you for your contributions.

[jihoonson]

Fixed in #9122.