Outbox router should skip heartbeat messages by default

Since Outbox is a router itself, it can do 2 things, either skip heartbeat messages or ignore them.

The previous behavior was to ignore them since the heartbeat messages were tombstones (so it automatically) happened.

After DBZ-1363 the Outbox SMT will try to direct the source to a wrong place, breaking things down.

I propose to do this in 2 steps:
1: Ignore the heartbeat messages
2: Adding an option to route them to somewhere else (possibly inheriting the configuration from the main connector itself)