Add `stateless_prewarm` thread pool name (#107674)

The stateless branch needs a new threadpool so we must add it here so
that we can permit it to perform blob-store operations.

server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java

@@ -182,6 +182,7 @@ public abstract class BlobStoreRepository extends AbstractLifecycleComponent imp
     public static final String STATELESS_TRANSLOG_THREAD_NAME = "stateless_translog";
     public static final String STATELESS_SHARD_WRITE_THREAD_NAME = "stateless_shard_write";
     public static final String STATELESS_CLUSTER_STATE_READ_WRITE_THREAD_NAME = "stateless_cluster_state";
+    public static final String STATELESS_SHARD_PREWARMING_THREAD_NAME = "stateless_prewarm";
 
     public static final String SNAPSHOT_PREFIX = "snap-";
 
@@ -2003,7 +2004,8 @@ public abstract class BlobStoreRepository extends AbstractLifecycleComponent imp
             STATELESS_SHARD_READ_THREAD_NAME,
             STATELESS_TRANSLOG_THREAD_NAME,
             STATELESS_SHARD_WRITE_THREAD_NAME,
-            STATELESS_CLUSTER_STATE_READ_WRITE_THREAD_NAME
+            STATELESS_CLUSTER_STATE_READ_WRITE_THREAD_NAME,
+            STATELESS_SHARD_PREWARMING_THREAD_NAME
         );
     }