Source: Add config option for mapping Couchbase collection to Kafka topic

Add a new source config property `couchbase.collection.to.topic`

Value is a list of key-value pairs where the key is the qualified name of a Couchbase collection ("scope.collection") and the value is the destination topic.

Example:

couchbase.collection.to.topic=scope1.collection1=topic1,scope2.collection2=topic2

Useful when the `couchbase.topic` property is not sufficient because the desired topic name differs from the collection name.