ExportedSnapshotter and InitialOnlySnapshotter should not always execute a snapshot.

When using SnapshotMode.EXPORTED, the connector is always executing a snapshot rather than transitioning to streaming mode after the initial exported snapshot completes successfully.

When using SnapshotMode.INITIAL_ONLY, the connector is always executing a snapshot. It should only perform a snapshot if no snapshot has been performed or if the prior snapshot step failed.