Bump post-recovery merge minimum version (#121997)

In #113462 we introduced a version bound on post-recovery merges to
avoid a spike of merge activity after an upgrade. At the time there was
no `IndexVersion` unique to the 9.x series, but we have such a version
now, so this commit properly restricts post-recovery merges to only
apply to indices created by versions that support them.

Relates ES-9620

server/src/internalClusterTest/java/org/elasticsearch/indices/recovery/IndexRecoveryIT.java

@@ -1967,7 +1967,14 @@ public class IndexRecoveryIT extends AbstractIndexRecoveryIntegTestCase {
         internalCluster().startMasterOnlyNode();
         final var dataNode = internalCluster().startDataOnlyNode();
         final var indexName = randomIdentifier();
-        createIndex(indexName, indexSettings(1, 0).put(INDEX_MERGE_ENABLED, false).build());
+        final var indexSettingsBuilder = indexSettings(1, 0).put(INDEX_MERGE_ENABLED, false);
+        if (randomBoolean()) {
+            indexSettingsBuilder.put(
+                IndexMetadata.SETTING_VERSION_CREATED,
+                IndexVersionUtils.randomVersionBetween(random(), IndexVersions.UPGRADE_TO_LUCENE_10_0_0, IndexVersion.current())
+            );
+        }
+        createIndex(indexName, indexSettingsBuilder.build());
 
         final var initialSegmentCount = 20;
         for (int i = 0; i < initialSegmentCount; i++) {
@@ -2051,7 +2058,7 @@ public class IndexRecoveryIT extends AbstractIndexRecoveryIntegTestCase {
                     IndexVersionUtils.randomVersionBetween(
                         random(),
                         IndexVersionUtils.getLowestWriteCompatibleVersion(),
-                        IndexVersionUtils.getPreviousVersion(IndexVersions.MERGE_ON_RECOVERY_VERSION)
+                        IndexVersionUtils.getPreviousVersion(IndexVersions.UPGRADE_TO_LUCENE_10_0_0)
                     )
                 )
                 .build()

server/src/main/java/org/elasticsearch/indices/PostRecoveryMerger.java

@@ -18,6 +18,7 @@ import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.concurrent.ThrottledTaskRunner;
 import org.elasticsearch.core.Releasable;
 import org.elasticsearch.core.Strings;
+import org.elasticsearch.core.UpdateForV10;
 import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.index.shard.IndexShard;
 import org.elasticsearch.index.shard.ShardId;
@@ -46,6 +47,7 @@ class PostRecoveryMerger {
     private static final boolean TRIGGER_MERGE_AFTER_RECOVERY;
 
     static {
+        @UpdateForV10(owner = UpdateForV10.Owner.DISTRIBUTED_INDEXING) // remove this escape hatch
         final var propertyValue = System.getProperty("es.trigger_merge_after_recovery");
         if (propertyValue == null) {
             TRIGGER_MERGE_AFTER_RECOVERY = true;
@@ -95,7 +97,7 @@ class PostRecoveryMerger {
             return recoveryListener;
         }
 
-        if (indexMetadata.getCreationVersion().before(IndexVersions.MERGE_ON_RECOVERY_VERSION)) {
+        if (indexMetadata.getCreationVersion().before(IndexVersions.UPGRADE_TO_LUCENE_10_0_0)) {
             return recoveryListener;
         }