[BUG] CreateIndexRequest deserializer is not working as expected

[owaiskazi19]

What is the bug?

Currently, we are deserializing the CreateIndexRequest using the _DESERIALIZER provided by java client

private String getAnomalyDetectorMappings() throws IOException {
        URL url = AnomalyDetectionIndices.class.getClassLoader().getResource(ANOMALY_DETECTORS_INDEX_MAPPING_FILE);
        return Resources.toString(url, Charsets.UTF_8);
    }

JsonpMapper mapper = sdkClient._transport().jsonpMapper();
        JsonParser parser = null;
        try {
            parser = mapper
                .jsonProvider()
                .createParser(new ByteArrayInputStream(getAnomalyDetectorMappings().getBytes(StandardCharsets.UTF_8)));
        } catch (Exception e) {
            e.printStackTrace();
        }

        CreateIndexRequest request = null;
        try {
            request = new CreateIndexRequest.Builder()
                .index(ANOMALY_DETECTORS_INDEX)
                .mappings(TypeMapping._DESERIALIZER.deserialize(parser, mapper))
                .build();
        } catch (Exception e) {
            e.printStackTrace();
        }

This results in adding index response with type object as below:

"featureAttributes": [
                        "com.google.common.collect.SingletonImmutableList",
                        [
                            {
                                "id": "rH6b9YQB_dnlYSXRWwUJ",
                                "name": "test",
                                "enabled": true,
                                "aggregation": {
                                    "@class": "org.opensearch.search.aggregations.metrics.SumAggregationBuilder",
                                    "name": "test",
                                    "metadata": {
                                        "@class": "java.util.Collections$EmptyMap"
                                    },
                                    "type": "sum",
                                    "writeableName": "sum",
                                    "pipelineAggregations": [
                                        "java.util.Collections$UnmodifiableCollection",
                                        []
                                    ],
                                    "subAggregations": [
                                        "java.util.Collections$UnmodifiableCollection",
                                        []
                                    ],
                                    "fragment": true
                                },
                                "fragment": false
                            }
                        ]
                    ],
                    "filterQuery": {
                        "@class": "org.opensearch.index.query.BoolQueryBuilder",
                        "writeableName": "bool",
                        "name": "bool",
                        "fragment": false
                    },
                    "detectionInterval": {
                        "@class": "org.opensearch.ad.model.IntervalTimeConfiguration",
                        "interval": 1,
                        "unit": "MINUTES",
                        "fragment": false
                    },
                    "windowDelay": {
                        "@class": "org.opensearch.ad.model.IntervalTimeConfiguration",
                        "interval": 1,
                        "unit": "MINUTES",
                        "fragment": false
                    },

Adding type object is creating issue while retrieving the index response for GetResponse API for java client.

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