alternator-test: add tests for incorrect JSON documents
alternator-test: add tests for incorrect JSON documents

The test case sends incorrectly formed JSON documents to alternator,
expecting a serialization exception as a response.

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