tests: add DEFAULT UNSET case to JSON cql tests
tests: add DEFAULT UNSET case to JSON cql tests

A case covering DEFAULT UNSET/DEFAULT NULL params is added
to json cql query test suite.

Refs #3909

scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla