Ignore error for catalog monitor for EH (#369)

CDC to Eventhub errors in SyncFlow with 'GetLastSyncBatchID not
supported for Eventhub', because in `flowable.go`'s `StartFlow` this
method is being called for catalog metrics.
Eventhub does not have this method implemented so we can just ignore the
error in this section and have sync ID in the metrics start from 0:
```Go
	if a.CatalogMirrorMonitor.IsActive() && len(records.Records) > 0 {
		syncBatchID, err := dest.GetLastSyncBatchID(input.FlowConnectionConfigs.FlowJobName)
		if err != nil && conn.Destination.Type != protos.DBType_EVENTHUB {
			return nil, err
		}
		....
	}
```

flow/activities/flowable.go

@@ -205,7 +205,7 @@ func (a *FlowableActivity) StartFlow(ctx context.Context, input *protos.StartFlo
 	}
 	if a.CatalogMirrorMonitor.IsActive() && len(records.Records) > 0 {
 		syncBatchID, err := dest.GetLastSyncBatchID(input.FlowConnectionConfigs.FlowJobName)
-		if err != nil {
+		if err != nil && conn.Destination.Type != protos.DBType_EVENTHUB {
 			return nil, err
 		}