Add CDC heartbeat to MySQL

[bleonard]

For Postgres, we worked on these issues:
#18987
#15040

The idea is to remove the need for the timeout that CDC is currently using to know to stop getting events. That was being triggered when Airbyte was subscribed to tables but not all of them, so that if there was a lot of acticity on one of the others, it would hit a timeout.

The goal for this issue is port that over to MySQL, as appropriate for the nuances that MySQL has.