Skip delete .plugins-ml-config system index during integ test (#1419)

Author: junqiu-lei

src/testFixtures/java/org/opensearch/knn/ODFERestTestCase.java

@@ -51,6 +51,7 @@
 
 import static org.opensearch.knn.TestUtils.KNN_BWC_PREFIX;
 import static org.opensearch.knn.TestUtils.OPENDISTRO_SECURITY;
+import static org.opensearch.knn.TestUtils.ML_PLUGIN_SYSTEM_INDEX_PREFIX;
 import static org.opensearch.knn.TestUtils.OPENSEARCH_SYSTEM_INDEX_PREFIX;
 import static org.opensearch.knn.TestUtils.SECURITY_AUDITLOG_PREFIX;
 import static org.opensearch.knn.TestUtils.SKIP_DELETE_MODEL_INDEX;
@@ -62,7 +63,12 @@
  */
 public abstract class ODFERestTestCase extends OpenSearchRestTestCase {
 
-    private final Set<String> IMMUTABLE_INDEX_PREFIXES = Set.of(KNN_BWC_PREFIX, SECURITY_AUDITLOG_PREFIX, OPENSEARCH_SYSTEM_INDEX_PREFIX);
+    private final Set<String> IMMUTABLE_INDEX_PREFIXES = Set.of(
+        KNN_BWC_PREFIX,
+        SECURITY_AUDITLOG_PREFIX,
+        OPENSEARCH_SYSTEM_INDEX_PREFIX,
+        ML_PLUGIN_SYSTEM_INDEX_PREFIX
+    );
 
     protected boolean isHttps() {
         return Optional.ofNullable(System.getProperty("https")).map("true"::equalsIgnoreCase).orElse(false);

src/testFixtures/java/org/opensearch/knn/TestUtils.java

@@ -99,6 +99,7 @@ public class TestUtils {
     public static final String UPGRADED_CLUSTER = "upgraded_cluster";
     public static final String SECURITY_AUDITLOG_PREFIX = "security-auditlog";
     public static final String OPENSEARCH_SYSTEM_INDEX_PREFIX = ".opensearch";
+    public static final String ML_PLUGIN_SYSTEM_INDEX_PREFIX = ".plugins-ml";
 
     // Generating vectors using random function with a seed which makes these vectors standard and generate same vectors for each run.
     public static float[][] randomlyGenerateStandardVectors(int numVectors, int dimensions, int seed) {