[8.x] Follow ups after Add Index Block API changes for N-2 support (#120537)

Changes in 8.x to allow regular indices in version N-2 to recover 
using the index.block.read_only too. 

Also makes the index.verified_read_only private.

Relates #120526

Author: tlrx

server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetadataVerifier.java

@@ -207,10 +207,11 @@ private static boolean isReadOnlyCompatible(
     }
 
     private static boolean hasIndexWritesBlock(IndexMetadata indexMetadata) {
-        if (IndexMetadata.INDEX_BLOCKS_WRITE_SETTING.get(indexMetadata.getSettings())) {
+        var indexSettings = indexMetadata.getSettings();
+        if (IndexMetadata.INDEX_BLOCKS_WRITE_SETTING.get(indexSettings) || IndexMetadata.INDEX_READ_ONLY_SETTING.get(indexSettings)) {
             return indexMetadata.isSearchableSnapshot()
                 || indexMetadata.getCreationVersion().isLegacyIndexVersion()
-                || MetadataIndexStateService.VERIFIED_READ_ONLY_SETTING.get(indexMetadata.getSettings());
+                || MetadataIndexStateService.VERIFIED_READ_ONLY_SETTING.get(indexSettings);
         }
         return false;
     }

server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexStateService.java

@@ -11,7 +11,6 @@
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-import org.elasticsearch.Build;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionListener;
@@ -121,8 +120,7 @@ public class MetadataIndexStateService {
         false,
         Setting.Property.IndexScope,
         Setting.Property.NotCopyableOnResize,
-        // Allow the setting to be updated in snapshot builds
-        Build.current().isSnapshot() ? Setting.Property.OperatorDynamic : Setting.Property.PrivateIndex
+        Setting.Property.PrivateIndex
     );
 
     private final ClusterService clusterService;