Default `gtid.new.channel.position` to earliest

I believe that the GTID new channel position setting should default to earliest not latest in order to prevent data loss by default.

If you have GTID of:

server-1:1-999

Then you fail over to server-2, and server-2 receives 100 writes:

server-1:1-99,server-2:1-100

Then DBZ connects... its offset is still:

server-1:1-999

So, it has to decide does it start GTID for server-2 at 1 or 1-100. It makes more sense to start with the earliest position in the binlog--default to data duplication not data loss.

See https://groups.google.com/forum/#!topic/debezium/mQanJ9mP0Eg for more discussion.