Omit writing global metadata if no change (#50901)

Uses the same optimization for the new cluster state storage layer as the old one, writing global
metadata only when changed. Avoids writing out the global metadata if none of the persistent
fields changed. Speeds up server:integTest by ~10%.

Relates #48701

Author: ywelsch

server/src/main/java/org/elasticsearch/gateway/PersistedClusterStateService.java

@@ -593,9 +593,11 @@ private void updateMetaData(MetaData previouslyWrittenMetaData, MetaData metaDat
             logger.trace("currentTerm [{}] matches previous currentTerm, writing changes only",
                 metaData.coordinationMetaData().term());
 
-            try (ReleasableDocument globalMetaDataDocument = makeGlobalMetaDataDocument(metaData)) {
-                for (MetaDataIndexWriter metaDataIndexWriter : metaDataIndexWriters) {
-                    metaDataIndexWriter.updateGlobalMetaData(globalMetaDataDocument.getDocument());
+            if (MetaData.isGlobalStateEquals(previouslyWrittenMetaData, metaData) == false) {
+                try (ReleasableDocument globalMetaDataDocument = makeGlobalMetaDataDocument(metaData)) {
+                    for (MetaDataIndexWriter metaDataIndexWriter : metaDataIndexWriters) {
+                        metaDataIndexWriter.updateGlobalMetaData(globalMetaDataDocument.getDocument());
+                    }
                 }
             }