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

Author: steveren

source/kafka-source.txt

@@ -216,6 +216,28 @@ an example source connector configuration file, see
        | **Default**: 16000
        | **Accepted Values**: An integer
 
+   * - copy.existing.pipeline
+     - list
+     - | An array of JSON objects describing the :manual:`pipeline operations
+         </core/aggregation-pipeline/>` to run when copying existing data.
+         This can improve the use of indexes by the copying manager and
+         make copying more efficient.
+
+         .. example::
+
+            In the following example, the :manual:`$match
+            </reference/operator/aggregation/match/>` aggregation operator
+            ensures that only documents in which the ``closed`` field is
+            set to ``false`` are copied.
+
+            .. code-block:: none
+
+               copy.existing.pipeline=[ { "$match": { "closed": "false" } } ]
+
+       |
+       | **Default**: ""
+       | **Accepted Values**: Valid aggregation pipeline stages
+
    * - errors.tolerance
      - string
      - | Whether to continue processing messages if an error is encountered.