Support MongoDB Oplog operations as config

In some cases, user not interested to listen to every event that happens on Oplog.
For example, the users only interested listen to only insert event or update event or both of them. It's a good idea to have a config like oplog.events that let the user select the events that he/she wants.
Whit this feature we can decrease the load on the Kafka cluster with large scale MongoDB cluster to filter the events that they are interested in.