[enhancement] Create a player `metadata` column

[BenBrostoff]

We expose a Player object that has props the optimizer needs to determine how to optimize. Users should have the option to 1) see any data they want in output and 2) create derived projections based on player props (ex. a weighted average of projections with a tuning for ownership). A metadata column of type dict could allow for this flexibility.

[BenBrostoff]

Completed via addition of kv_store property