Make FixedSizedList Json serializable

[colin99d]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
I would like for the arrow-json library to automatically implement the FixedSizedList.

Describe the solution you'd like
It seems like adding FixedSizedList should be trivial, since it would be encoded in the same way as a list, I would be happy to try it myself, I just wanted to start this first to make sure there is nothing I am missing.

Describe alternatives you've considered
The alternative is I continue to implement this manually.

[Russ741]

I'd like to work on this issue.

[tustvold]

label_issue.py automatically added labels {'arrow'} from #5646