[Ballista] Fill functional gaps between datafusion and ballista

[Ted-Jiang]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Current Ballista implementation is more like standalone system that able to run the Datafusion operators in a distributed way.
But threr are some gaps between them.

Currently we need fix:

• UnionAll support for Ballista #2032
• [Ballista] datafusion-cli with ballista not support show tables and show columns  #1984
• [Ballista] Support more ScalarFunction in Ballista #2007
• [Ballista] support datafusion built_in UDAF work in ballista cluster #1985
• Support substring with three arguments: (str, from, for) for DataFrame API and Ballista #2092
• Enable explain query in Ballista. #2096
• [Ballista] Make PhysicalAggregateExprNode has repeated PhysicalExprNode #2180

Welcome to add missing part 😊!

Describe the solution you'd like

Describe alternatives you've considered
Maybe we can find a solution to find functions that are missed in the ballista but implemented in the datafusion automatically.

[yjshen]

I've updated the list above with a substr item.