Adding new API to register backward compatible class names

Author: xiangfu0

pinot-spi/src/main/java/org/apache/pinot/spi/plugin/PluginManager.java

@@ -496,4 +496,9 @@ public void registerRecordReaderClass(String inputFormat, String recordReaderCla
       INPUT_FORMAT_TO_RECORD_READER_CONFIG_CLASS_NAME_MAP.put(inputFormat.toLowerCase(), recordReaderConfigClass);
     }
   }
+
+  // Register plugin class names when users try to deprecate old plugins/libraries.
+  public void registerBackwardCompatibleClassName(String oldClassName, String newClassName) {
+    PLUGINS_BACKWARD_COMPATIBLE_CLASS_NAME_MAP.put(oldClassName, newClassName);
+  }
 }