[hotfix] Make paimonConfig of PaimonLakeStorage protected in case a subclass needs to use it (apache#1916)

Author: LiebingYu

fluss-lake/fluss-lake-paimon/src/main/java/org/apache/fluss/lake/paimon/PaimonLakeStorage.java

@@ -31,7 +31,7 @@
 /** Paimon implementation of {@link LakeStorage}. */
 public class PaimonLakeStorage implements LakeStorage {
 
-    private final Configuration paimonConfig;
+    protected final Configuration paimonConfig;
 
     public PaimonLakeStorage(Configuration configuration) {
         this.paimonConfig = configuration;