[FEA] make cudf to_json engine=cudf as default

libcudf has write_json that works for both json lines=true/false and orient="records". default engine=auto triggers CPU pandas `to_json` which shows a warning.

**Missing Pandas Feature Request**
A clear and concise summary of the pandas function(s) you'd like to be able run with cuDF.
https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.to_json.html
If there are missing features in libcudf write_json to enable this, file issues for them.

**Profiler Output**
Warning "Using CPU via Pandas to write JSON dataset"