Add serialization for entire LogicalPlans to datafusion-proto

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

In order to serialize subquery expressions (#4337) we would need to serialize entire LogicalPlans which datafusion-proto does not do .

Describe the solution you'd like
I would like to have the ability to serialize / deserialize LogicalPlans in the datafusion. I believe we can take a friendly look / downright copy this code from ballista:

https://github.com/apache/arrow-ballista/blob/acbdf608807697e72122a249c4bf7505274906d0/ballista/core/proto/datafusion.proto

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
#4337

cc @andygrove @thinkharderdev @avantgardnerio

I am marking this as "good first isseu" because I think it would mostly be an exercise in porting code and tests from one repo to another.

[l0kr]

Let me take a stab at this. @alamb anything changed since this task was created?

[alamb]

THanks @l0kr -- sorry for the old ticket. I think this task is actually is mostly done https://github.com/apache/arrow-datafusion/tree/main/datafusion/proto/src/logical_plan

It would be very valuable if you were able to go through and fill out the various "Not implemented" in the plan conversion.

Closing