[BUG] Issue with percolate query transforming documents with object type fields

[eirsep]

Mapping

{
  "mappings": {
    "properties": {
      "something.a.b": { "type": "long" }
    }
  }
}

Document that the monitor is not able to recognize but the index ingests correctly based on. the mapping

{
    "something": {
        "a" : {
            "b" : 123
        }
    }
}

Document that the monitor is able to recognize and trigger

{
    "something.a.b" : 123
}

Doc-level monitor spec

{
						"type": "monitor",
						"schema_version": 1,
						"name": "test",
						"monitor_type": "doc_level_monitor",
						"enabled": true,
						"enabled_time": 1680126087150,
						"schedule": {
							"period": {
								"interval": 1,
								"unit": "MINUTES"
							}
						},
						"inputs": [{
							"doc_level_input": {
								"description": "test",
								"indices": [
									"i3"
								],
								"queries": [{

										"name": "78b3756a-7804-4ef7-8555-7b9024a02d2d",
										"query": "(something.a.b:123)",
										"tags": [
											"low",
											"cloudtrail",
											"attack.exfiltration",
											"attack.t1537"
										]
									}
								]
							}
						}],
						"triggers": [{
							"document_level_trigger": {
								"id": "FY5RL4cBirpptBbLj0ju",
								"name": "CW Trail Alert",
								"severity": "1",
								"condition": {
									"script": {
										"source": "(query[tag=cloudtrail])",
										"lang": "painless"
									}
								}
							}
						}]
					
					}

[eirsep]

We need to consciously handle transformation logic for null values and array type values also

[eirsep]

Field transform logic at needs to be fixed

alerting/alerting/src/main/kotlin/org/opensearch/alerting/DocumentLevelMonitorRunner.kt

Lines 563 to 575 in 3f2e651

	return hits.map { hit ->
	val sourceMap = hit.sourceAsMap
	var xContentBuilder = XContentFactory.jsonBuilder().startObject()
	sourceMap.forEach { (k, v) ->
	xContentBuilder = xContentBuilder.field("${k}_${index}_$monitorId", v)
	}
	xContentBuilder = xContentBuilder.endObject()
	val sourceRef = BytesReference.bytes(xContentBuilder)
	Pair(hit.id, sourceRef)
	}

[lezzago]

PR has been merged, but backports failed