Modify DeleteStep to allow deletion of other indices

Currently, the `DeleteStep` is only able to delete the index that ILM
runs on. By accepting a target index name supplier, we can use it to
delete other indices as well.

Author: nielsbauman

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/DeleteStep.java

@@ -16,26 +16,56 @@
 import org.elasticsearch.cluster.metadata.DataStream;
 import org.elasticsearch.cluster.metadata.IndexAbstraction;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
+import org.elasticsearch.cluster.metadata.LifecycleExecutionState;
 import org.elasticsearch.cluster.metadata.ProjectMetadata;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.index.Index;
 
+import java.util.function.BiFunction;
+
 /**
  * Deletes a single index.
  */
 public class DeleteStep extends AsyncRetryDuringSnapshotActionStep {
+
     public static final String NAME = "delete";
     private static final Logger logger = LogManager.getLogger(DeleteStep.class);
+    private static final BiFunction<String, LifecycleExecutionState, String> DEFAULT_TARGET_INDEX_NAME_SUPPLIER = (
+        indexName,
+        lifecycleState) -> indexName;
+
+    private final BiFunction<String, LifecycleExecutionState, String> targetIndexNameSupplier;
+    private final boolean indexSurvives;
 
+    /**
+     * Use this constructor to delete the index that ILM is currently operating on.
+     */
     public DeleteStep(StepKey key, StepKey nextStepKey, Client client) {
+        this(key, nextStepKey, client, DEFAULT_TARGET_INDEX_NAME_SUPPLIER, false);
+    }
+
+    /**
+     * Use this constructor to delete a specific index, potentially different from the one that ILM is currently operating on. The parameter
+     * {@code indexSurvives} indicates whether the index that ILM runs on will survive (i.e. not get deleted) this step.
+     * Look at the callers of {@link AsyncActionStep#indexSurvives()} for more details.
+     */
+    public DeleteStep(
+        StepKey key,
+        StepKey nextStepKey,
+        Client client,
+        BiFunction<String, LifecycleExecutionState, String> targetIndexNameSupplier,
+        boolean indexSurvives
+    ) {
         super(key, nextStepKey, client);
+        this.targetIndexNameSupplier = targetIndexNameSupplier;
+        this.indexSurvives = indexSurvives;
     }
 
     @Override
     public void performDuringNoSnapshot(IndexMetadata indexMetadata, ProjectMetadata currentProject, ActionListener<Void> listener) {
         String policyName = indexMetadata.getLifecyclePolicyName();
-        String indexName = indexMetadata.getIndex().getName();
+        String indexName = targetIndexNameSupplier.apply(indexMetadata.getIndex().getName(), indexMetadata.getLifecycleExecutionState());
         IndexAbstraction indexAbstraction = currentProject.getIndicesLookup().get(indexName);
         assert indexAbstraction != null : "invalid cluster metadata. index [" + indexName + "] was not found";
         DataStream dataStream = indexAbstraction.getParentDataStream();
@@ -88,7 +118,7 @@ public void performDuringNoSnapshot(IndexMetadata indexMetadata, ProjectMetadata
 
     @Override
     public boolean indexSurvives() {
-        return false;
+        return indexSurvives;
     }
 
     @Override