Align DataConverter with Go Client

[natemort]

What changed?

• Make DataConverter match Go rather than Java.

Why?

• The Go DataConverter's approach is unique and potentially difficult to parse. But it's unambiguous. The Java client either wraps the input into a json array, or encodes it as-is if there's a single value. This ends up being ambiguous as to how it should be decoded any time a List is one of the arguments.
• We could alternatively always wrap the arguments into a list, but introducing a third standard seems worse.

How did you test it?

• Unit tests

Potential risks

• None

Release notes

Documentation Changes

[timl3136]

LGTM