Add support for physical operators serde

[Kikkon]

Originally posted by @andygrove in #4390 (comment)

[Kikkon]

🥲 I don't seem to find any code related to serde of physical operators in ballista, it looks like it's just done when serde physical plan (maybe I am not very familiar with datafusion ), do we need to add serde of physical operators? cc @andygrove