Incoporate PR review feedback

Signed-off-by: Ashish Singh <ssashish@amazon.com>

server/src/main/java/org/opensearch/index/remote/RemoteStoreUtils.java

@@ -106,23 +106,14 @@ public static void verifyNoMultipleWriters(List<String> mdFiles, Function<String
     /**
      * Converts an input hash which occupies 64 bits of space into Base64 (6 bits per character) String. This must not
      * be changed as it is used for creating path for storing remote store data on the remote store.
-     */
-    static String longToBase64(long value) {
-        byte[] hashBytes = ByteBuffer.allocate(Long.BYTES).putLong(value).array();
-        return base64(hashBytes);
-    }
-
-    /**
      * This converts the byte array to base 64 string. `/` is replaced with `_`, `+` is replaced with `-` and `=`
      * which is padded at the last is also removed. These characters are either used as delimiter or special character
      * requiring special handling in some vendors. The characters present in this base64 version are [A-Za-z0-9_-].
      * This must not be changed as it is used for creating path for storing remote store data on the remote store.
-     *
-     * @param bytes byte array
-     * @return base 64 string.
      */
-    private static String base64(byte[] bytes) {
-        String base64 = Base64.getEncoder().encodeToString(bytes);
-        return base64.substring(0, base64.length() - 1).replace('/', '_').replace('+', '-');
+    static String longToBase64(long value) {
+        byte[] hashBytes = ByteBuffer.allocate(Long.BYTES).putLong(value).array();
+        String base64Str = Base64.getUrlEncoder().encodeToString(hashBytes);
+        return base64Str.substring(0, base64Str.length() - 1);
     }
 }

server/src/main/java/org/opensearch/indices/IndicesService.java

@@ -312,7 +312,7 @@ public class IndicesService extends AbstractLifecycleComponent
      */
     public static final Setting<PathType> CLUSTER_REMOTE_STORE_PATH_PREFIX_TYPE_SETTING = new Setting<>(
         "cluster.remote_store.index.path.prefix.type",
-        PathType.HASHED_PREFIX.toString(),
+        PathType.FIXED.toString(),
         PathType::parseString,
         Property.NodeScope,
         Property.Dynamic