Support DateTime2 data type for TimeStamp column

[stedel]

The sink supports SqlDbType DateTime2 in custom columns without problems. The TimeStamp column does not support it yet though.
Setting the data type manually on the TimeStamp object yields a InvalidCastException when the Sink is trying to flush the log entries. Enabling SelfLog logs: Unable to write 1 log events to the database due to following error: Unable to cast object of type 'System.DateTime' to type 'System.DateTimeOffset'.

The underlying database uses DateTime2 in the TimeStamp column instead of the default DateTime or recently supportedDateTimeOffset.

I don't see a reason, why DateTime2 should not be supported on TimeStamp. As discussed in #187 this addition does not affect the defaults and therefore should be backwards compatible.