Adjust init map size of user data of index commit (#40965)

The number of user data attributes of an index commit has increased 
from 6 to 8, but we forgot to adjust. This change increases the initial 
size of that map to avoid resizing.

server/src/main/java/org/elasticsearch/index/engine/InternalEngine.java

@@ -2357,7 +2357,7 @@ public class InternalEngine extends Engine {
                  * {@link IndexWriter#commit()} call flushes all documents, we defer computation of the maximum sequence number to the time
                  * of invocation of the commit data iterator (which occurs after all documents have been flushed to Lucene).
                  */
-                final Map<String, String> commitData = new HashMap<>(6);
+                final Map<String, String> commitData = new HashMap<>(8);
                 commitData.put(Translog.TRANSLOG_GENERATION_KEY, translogFileGeneration);
                 commitData.put(Translog.TRANSLOG_UUID_KEY, translogUUID);
                 commitData.put(SequenceNumbers.LOCAL_CHECKPOINT_KEY, localCheckpointValue);
@@ -2603,7 +2603,7 @@ public class InternalEngine extends Engine {
      * Gets the commit data from {@link IndexWriter} as a map.
      */
     private static Map<String, String> commitDataAsMap(final IndexWriter indexWriter) {
-        Map<String, String> commitData = new HashMap<>(6);
+        final Map<String, String> commitData = new HashMap<>(8);
         for (Map.Entry<String, String> entry : indexWriter.getLiveCommitData()) {
             commitData.put(entry.getKey(), entry.getValue());
         }