Make CoordinatorGroupCommitKeyManipulator public to reuse the logic i…

…n other projects (#1864)

core/src/main/java/com/scalar/db/transaction/consensuscommit/CoordinatorGroupCommitter.java

@@ -35,7 +35,7 @@ public static boolean isEnabled(ConsensusCommitConfig config) {
     return config.isCoordinatorGroupCommitEnabled();
   }
 
-  static class CoordinatorGroupCommitKeyManipulator
+  public static class CoordinatorGroupCommitKeyManipulator
       implements KeyManipulator<String, String, String, String, String> {
     private static final int PRIMARY_KEY_SIZE = 24;
     private static final char DELIMITER = ':';