Maintain step order for ILM trace logging (#39522)

When trace logging is enabled we log the computed steps for a policy. This
commit makes sure that the steps that are logged are in the same order they will
be run when the policy executes. This makes it much easier to reason about the
policy if the move-to-step API is ever required in the future.

x-pack/plugin/ilm/src/main/java/org/elasticsearch/xpack/indexlifecycle/PolicyStepsRegistry.java

@@ -39,6 +39,7 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -125,7 +126,7 @@ public LifecyclePolicyMetadata read(StreamInput in, String key) {
                 List<Step> policyAsSteps = policyMetadata.getPolicy().toSteps(policyClient);
                 if (policyAsSteps.isEmpty() == false) {
                     firstStepMap.put(policyMetadata.getName(), policyAsSteps.get(0));
-                    final Map<Step.StepKey, Step> stepMapForPolicy = new HashMap<>();
+                    final Map<Step.StepKey, Step> stepMapForPolicy = new LinkedHashMap<>();
                     for (Step step : policyAsSteps) {
                         assert ErrorStep.NAME.equals(step.getKey().getName()) == false : "unexpected error step in policy";
                         stepMapForPolicy.put(step.getKey(), step);