Add execute_logical_plan method to Ballista context

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Once #970 is merged, we have a functional Python client again, but it only supports SQL and not the DataFrame API.

If we add an execute_logical_plan method to the Ballista context then users can use the DataFusion Python API to build logical plans and then execute them via the Ballista context.

Describe the solution you'd like

• Add execute_logical_plan method to Ballista Rust context
• Add execute_logical_plan method to Ballista Python context

Describe alternatives you've considered

Additional context