DOCSP-10924: add new id strategy configuration - overwrite existing (#34)

Author: Chris Cho

source/kafka-sink-properties.txt

@@ -93,6 +93,13 @@ data to sink to MongoDB. For an example configuration file, see
        | **Default**: ``com.mongodb.kafka.connect.sink.processor.id.strategy.BsonOidStrategy``
        | **Accepted Values**: An empty string or a fully qualified Java class name
 
+   * - document.id.strategy.overwrite.existing
+     - boolean
+     - | Whether the connector should overwrite existing values in the ``_id`` field when the strategy defined in ``document.id.strategy`` is applied.
+       |
+       | **Default**: ``true``
+       | **Accepted Values**: ``true`` or ``false``
+   
    * - delete.on.null.values
      - boolean
      - | Whether the connector should delete documents with matching key values when value is null.