Substrait ExecutionPlan Serialization

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
Serialize physical plans, AKA, `ExecutionPlan`s as Substrait plans.

**Describe the solution you'd like**
Expose Substrait consumers and producers for `ExecutionPlan` to allow for encoding to and decoding to / from Substrait.

**Describe alternatives you've considered**
Using LogicalPlans only.

Start by locating the Python bindings for ExecutionPlan and any existing Substrait support for LogicalPlans. Review how current plan consumers and producers are exposed, then define the encoding and decoding boundaries for physical plans. Done means ExecutionPlans can be encoded to and decoded from Substrait plans.

Written by the indexing model from the issue text.