Kafka connectors: new group ID field (#392)

Author: Paul-Cornell

snippets/general-shared-text/kafka-cli-api.mdx

@@ -22,5 +22,8 @@ If you use Kafka API keys and secrets for authentication:
 Additional settings include:
 
 - `--confluent` (CLI) or `confluent` (Python): True to indicate that the cluster is running Confluent Kafka.
-- `--num-messages-to-consume` (CLI) or `num_messages_to_consume` (Python): The maximum number of messages to get from the topic. The default is `1`.
-- `--timeout` (CLI) or `timeout` (Python): The maximum amount of time to wait for the response of a request to the topic, expressed in seconds. The default is `1.0`.
+- `--num-messages-to-consume` (CLI) or `num_messages_to_consume` (Python): The maximum number of messages to get from the topic. The default is `1` if not otherwise specified.
+- `--timeout` (CLI) or `timeout` (Python): The maximum amount of time to wait for the response of a request to the topic, expressed in seconds. The default is `1.0` if not otherwise specified.
+- `--group-id` (CLI) or `group_id` (Python): The ID of the consumer group, if any, that is associated with the target Kafka cluser. 
+  (A consumer group is a way to allow a pool of consumers to divide the consumption of data 
+  over topics and partitions.) The default is `default_group_id` if not otherwise specified.