Keep SnapshotReaderMetrics bean registered after snapshot completed

There are certain metrics that we want to retrieve after the snapshot has completed. However, the SnapshotReaderMetrics bean is immediately unregistered when the snapshot completes.

Because of this, we have found it is unreliable to retrieve certain valuable metrics that are only available at the the end of the snapshot. Such as getSnapshotCompleted(), getSnapshotDurationInSeconds(), getSnapshotAborted() etc.

Sometimes the snapshot completes so quickly that we are unable to connect to the bean at all while it is still up.

Solution: After the initial snapshot, the SnapshotReader MX bean should remain registered until the next connector restart.