Implement protobuf serialization for LogicalPlan::CopyTo

[andygrove]

Is your feature request related to a problem or challenge?

Ballista can no longer write query results to disk, because of refactoring of the logical plan in DataFusion to use CopyTo and there is no serde support for this node, resulting in this error:

Error: DataFusionError(Internal("failed to serialize logical plan: Internal(\"LogicalPlan serde is not yet implemented for Copy\")"))

Describe the solution you'd like

Implement serde for CopyTo

Describe alternatives you've considered

No response

Additional context

No response