Refactor MetadataService to Use ContentTransformer

Motivation:
Previously, the Central Dogma server in `MetadataService` would repeatedly attempt to commit until it succeeded. With the introduction of `ContentTransformer` in line#1064, the server can now handle transformations in a single attempt, avoiding unnecessary retries.

Modifications:
- Updated `MetadataService` to utilize `ContentTransformer` for commit operations.

Result:
- Improved efficiency in `MetadataService` by eliminating repeated commit attempts.

common/src/main/java/com/linecorp/centraldogma/common/RedundantChangeException.java

@@ -16,37 +16,33 @@
 
 package com.linecorp.centraldogma.common;
 
+import static java.util.Objects.requireNonNull;
+
+import javax.annotation.Nullable;
+
 /**
  * A {@link CentralDogmaException} that is raised when attempted to push a commit without effective changes.
  */
 public class RedundantChangeException extends CentralDogmaException {
 
     private static final long serialVersionUID = 8739464985038079688L;
-
-    /**
-     * Creates a new instance.
-     */
-    public RedundantChangeException() {}
+    @Nullable
+    private final Revision headRevision;
 
     /**
      * Creates a new instance.
      */
     public RedundantChangeException(String message) {
         super(message);
+        headRevision = null;
     }
 
     /**
      * Creates a new instance.
      */
-    public RedundantChangeException(Throwable cause) {
-        super(cause);
-    }
-
-    /**
-     * Creates a new instance.
-     */
-    public RedundantChangeException(String message, Throwable cause) {
-        super(message, cause);
+    public RedundantChangeException(Revision headRevision, String message) {
+        super(message);
+        this.headRevision = requireNonNull(headRevision, "headRevision");
     }
 
     /**
@@ -57,13 +53,15 @@ public RedundantChangeException(String message, Throwable cause) {
      */
     public RedundantChangeException(String message, boolean writableStackTrace) {
         super(message, writableStackTrace);
+        headRevision = null;
     }
 
     /**
-     * Creates a new instance.
+     * Returns the head revision of the repository when this exception was raised.
      */
-    protected RedundantChangeException(String message, Throwable cause, boolean enableSuppression,
-                                       boolean writableStackTrace) {
-        super(message, cause, enableSuppression, writableStackTrace);
+    public Revision headRevision() {
+        // This is only called from the server-side which always sets the head revision.
+        assert headRevision != null;
+        return headRevision;
     }
 }

server/src/main/java/com/linecorp/centraldogma/server/internal/storage/repository/git/CommitExecutor.java

@@ -156,10 +156,12 @@ RevisionAndEntries commit(@Nullable Revision prevRevision, Revision nextRevision
             }
 
             if (!allowEmptyCommit && isEmpty) {
+                // prevRevision is not null when allowEmptyCommit is false.
+                assert prevRevision != null;
                 throw new RedundantChangeException(
+                        prevRevision,
                         "changes did not change anything in " + gitRepository.parent().name() + '/' +
-                        gitRepository.name() + " at revision " +
-                        (prevRevision != null ? prevRevision.major() : 0) + ": " + changes);
+                        gitRepository.name() + " at revision " + prevRevision.major() + ": " + changes);
             }
 
             // flush the current index to repository and get the result tree object id.