Support DataFrame.collect for Ballista DataFrames

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
A DataFrame from a BallistaContext should work just like a DataFrame from a DataFusion ExecutionContext. The user should be able to directly call execution methods such as collect.

Describe the solution you'd like
A DataFrame from a BallistaContext should work just like a DataFrame from a DataFusion ExecutionContext. The user should be able to directly call execution methods such as collect.

Describe alternatives you've considered
None

Additional context
N/A