DOCSP-12146: [KAFKA] Copy existing configuration with pipeline

Author: steveren

source/kafka-source.txt

@@ -157,7 +157,7 @@ an example source connector configuration file, see
        .. seealso:: :ref:`Multiple source example <multi-source-example>`.
 
        | **Default**: []
-       | **Accepted Values**: A valid JSON array
+       | **Accepted Values**: Valid aggregation pipeline stages
 
    * - collation
      - string
@@ -235,7 +235,7 @@ an example source connector configuration file, see
                copy.existing.pipeline=[ { "$match": { "closed": "false" } } ]
 
        |
-       | **Default**: ""
+       | **Default**: []
        | **Accepted Values**: Valid aggregation pipeline stages
 
    * - errors.tolerance