MINOR: Preserve backwards-compatibility by renaming the AlterPartitionReassignment metric to PartitionReassignment

In 18d4e57f6e (diff-394389922df5210adf43a8b7064cc4ffL61) we unintentionally renamed the metric with the previous changes to reassignments

Author: Stanislav Kozlovski <stanislav_kozlovski@outlook.com>

Reviewers: Manikumar Reddy <manikumar.reddy@gmail.com>

Closes #7606 from stanislavkozlovski/minor-partition-reassignment-metric

core/src/main/scala/kafka/controller/ControllerState.scala

@@ -60,6 +60,8 @@ object ControllerState {
 
   case object AlterPartitionReassignment extends ControllerState {
     def value = 5
+
+    override def rateAndTimeMetricName: Option[String] = Some("PartitionReassignmentRateAndTimeMs")
   }
 
   case object AutoLeaderBalance extends ControllerState {