Route analytics queries by index setting, not table-name prefix

Today `RestUnifiedQueryAction.isAnalyticsIndex` dispatches to the analytics
engine when the source index name starts with `parquet_`. That's brittle —
it conflates naming convention with storage type. An index created without
the prefix but with pluggable dataformat enabled is silently sent to the
Lucene path; an index named `parquet_foo` without the setting is
mis-dispatched to analytics.

Use the authoritative signal instead: the `index.pluggable.dataformat.enabled`
setting on cluster-state metadata. This is the same setting integration tests
(`CoordinatorReduceIT`, `CompositeCommitDeletionIT`, etc.) already use to
create analytics-backed indices, and it's what `FieldStorageResolver` reads
to decide field-level storage.

Behavior:
- `index.pluggable.dataformat.enabled=true`  → analytics engine (DataFusion)
- flag absent / false / index missing         → Calcite→OpenSearch DSL path

Signed-off-by: bowenlan-amzn <bowenlan23@gmail.com>

Author: bowenlan-amzn

plugin/src/main/java/org/opensearch/sql/plugin/rest/RestUnifiedQueryAction.java

@@ -76,7 +76,7 @@ public RestUnifiedQueryAction(
   /**
    * Returns true iff the target index has {@link
    * IndexSettings#PLUGGABLE_DATAFORMAT_ENABLED_SETTING} set and {@link
-   * IndexSettings#PLUGGABLE_DATAFORMAT_VALUE_SETTING} is {@code "parquet"}, routing it to
+   * IndexSettings#PLUGGABLE_DATAFORMAT_VALUE_SETTING} is {@code "composite"}, routing it to
    * DataFusion instead of the Calcite→DSL path.
    *
    * <p>Note: This creates a separate UnifiedQueryContext for parsing. The context cannot be shared
@@ -110,7 +110,7 @@ private boolean isPluggableDataformatIndex(String indexName) {
     }
     var settings = indexMetadata.getSettings();
     return IndexSettings.PLUGGABLE_DATAFORMAT_ENABLED_SETTING.get(settings)
-        && "parquet".equals(IndexSettings.PLUGGABLE_DATAFORMAT_VALUE_SETTING.get(settings));
+        && "composite".equals(IndexSettings.PLUGGABLE_DATAFORMAT_VALUE_SETTING.get(settings));
   }
 
   /** Execute a query through the unified query pipeline on the sql-worker thread pool. */

plugin/src/test/java/org/opensearch/sql/plugin/rest/RestUnifiedQueryActionTest.java

@@ -25,7 +25,7 @@
 
 /**
  * Tests for analytics index routing in RestUnifiedQueryAction. Routing requires both {@code
- * index.pluggable.dataformat.enabled=true} and {@code index.pluggable.dataformat=parquet}.
+ * index.pluggable.dataformat.enabled=true} and {@code index.pluggable.dataformat=composite}.
  */
 public class RestUnifiedQueryActionTest {
 
@@ -57,7 +57,7 @@ public void pluggableDataformatIndexRoutesToAnalytics() {
         "parquet_logs",
         Settings.builder()
             .put(IndexSettings.PLUGGABLE_DATAFORMAT_ENABLED_SETTING.getKey(), true)
-            .put(IndexSettings.PLUGGABLE_DATAFORMAT_VALUE_SETTING.getKey(), "parquet")
+            .put(IndexSettings.PLUGGABLE_DATAFORMAT_VALUE_SETTING.getKey(), "composite")
             .build());
 
     assertTrue(action.isAnalyticsIndex("source = parquet_logs | fields ts", QueryType.PPL));