Add compability for 1.9 last savepoint info on upgrade/recovery

With FLINK-35265, a new field in JobStatus was introduced called `upgradeSnapshotReference`. This works for new jobs submitted to the operator, but jobs that were submitted to versions before this commit will not be able to upgrade because it used to use `status.jobStatus.savepointInfo.lastSavepoint` field.

The operator should be able to fallback to the old field if found to ensure a smooth upgrade process for Flink jobs when upgrading to the new operator version.