Add reindex_required flag to index version deprecation notice response

Author: lukewhiting

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/IndexDeprecationChecks.java

@@ -20,6 +20,7 @@
 import org.elasticsearch.xpack.core.deprecation.DeprecationIssue;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -43,7 +44,7 @@ static DeprecationIssue oldIndicesCheck(IndexMetadata indexMetadata, ClusterStat
                 "https://www.elastic.co/guide/en/elasticsearch/reference/master/breaking-changes-9.0.html",
                 "This index has version: " + currentCompatibilityVersion.toReleaseVersion(),
                 false,
-                null
+                Collections.singletonMap("reindex_required", true)
             );
         }
         return null;

x-pack/plugin/deprecation/src/test/java/org/elasticsearch/xpack/deprecation/IndexDeprecationChecksTests.java

@@ -29,6 +29,7 @@
 import java.util.Map;
 
 import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
 import static org.elasticsearch.xpack.deprecation.DeprecationChecks.INDEX_SETTINGS_CHECKS;
 import static org.hamcrest.Matchers.empty;
 import static org.hamcrest.Matchers.equalTo;
@@ -52,7 +53,7 @@ public void testOldIndicesCheck() {
             "https://www.elastic.co/guide/en/elasticsearch/reference/master/breaking-changes-9.0.html",
             "This index has version: " + createdWith.toReleaseVersion(),
             false,
-            null
+            singletonMap("reindex_required", true)
         );
         List<DeprecationIssue> issues = DeprecationChecks.filterChecks(INDEX_SETTINGS_CHECKS, c -> c.apply(indexMetadata, clusterState));
         assertEquals(singletonList(expected), issues);