Add JSON integration tests to LLCRealtimeClusterIntegrationTest

There seems to be some issues in the code path that ingest JSON data for REALTIME tables.

If data like the following gets ingested from Kafka:
"EvaluationResult" : {
"AssertionEvaluationResult" : {
"summary" : {
"passed" : 0,
"failed" : 0,
"warned" : 0,
"overallStatus" : "XXXX"
},
"evaluatedAssertions" : [ ]
}
}

The nested empty array gets turned into a NULL in pinot DB, expected behavior would be we get an empty array in Pinot:


Start with LLCRealtimeClusterIntegrationTest and trace its realtime JSON ingestion setup for Kafka input. Add coverage for the nested empty evaluatedAssertions array, then verify the integration test preserves it as an empty array rather than NULL in Pinot.

Written by the indexing model from the issue text.