Add RemoteSegmentStoreDirectory to interact with remote segment store

Signed-off-by: Sachin Kale <kalsac@amazon.com>

server/src/main/java/org/opensearch/index/store/RemoteDirectory.java

@@ -33,7 +33,7 @@
  *
  * @opensearch.internal
  */
-public final class RemoteDirectory extends Directory {
+public class RemoteDirectory extends Directory {
 
     private final BlobContainer blobContainer;
 
@@ -50,6 +50,16 @@ public String[] listAll() throws IOException {
         return blobContainer.listBlobs().keySet().stream().sorted().toArray(String[]::new);
     }
 
+    /**
+     * Returns names of files with given prefix in this directory.
+     * @param filenamePrefix The prefix to match against file names in the directory
+     * @return A list of the matching filenames in the directory
+     * @throws IOException IOException if there were any failures in reading from the blob container
+     */
+    public Collection<String> listFilesByPrefix(String filenamePrefix) throws IOException {
+        return blobContainer.listBlobsByPrefix(filenamePrefix).keySet();
+    }
+
     /**
      * Removes an existing file in the directory.
      *