Enhance the `couchbase.topic.to.collection` feature to support specifying the target bucket as well as scope and collection.

For example, allow something like this:

In this example, records from topic `topic-a` would be written to scope `myScope` collection `myCollection` in the default bucket (specified by the existing `couchbase.bucket` config property).

Records from `topic-b` would be written to scope `otherScope` collection `otherCollection` in bucket `otherBucket`.

In other words, the collection specifier should allow an optional bucket prefix, delimited with a colon.

https://docs.couchbase.com/kafka-connector/current/sink-configuration-options.html#couchbase.topic.to.collection