Plans with tables from TableProviderFactorys can't be serialized

[avantgardnerio]

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

We recently add TableProviderFactorys to allow registration of tables by users at run time (i.e. CREATE EXTERNAL TABLE dt STORED AS DELTATABLE). However, the resulting logical plans (select * from dt) can't be shipped between nodes (i.e. ballista client & scheduler) due to lack of ability to serde them.

Describe the solution you'd like

1. Create a CustomTable provider that contains the information necessary to reify the table on a different node (as long as it has the same TableProviderFactory registered).
2. Add serde logic to make use of the CustomTable

Describe alternatives you've considered

It's all pretty confusing, but I think this is the way forward for logical plans to be extendable by 3rd parties at runtime. I'm open to other suggestions though.