fix: Fix README.md Default value for maxBufferBytes (#412)

Looking at the code the current Default value for maxBufferBytes is 9500000L (DEFAULT_MAX_BUFFER_BYTES)
(https://github.com/googleapis/java-pubsub-group-kafka-connector/blob/main/src/main/java/com/google/pubsub/kafka/sink/CloudPubSubSinkConnector.java#L53)
9500000L is also the max value that can be used.

Fix [411](#411)

Author: DanielssonJacob

README.md

@@ -199,7 +199,7 @@ configurations:
 | cps.project                | String                        | REQUIRED (No default)       | The project containing the Pub/Sub topic, e.g. "bar" from above.                                                                                                                                                                                                                                                                    |
 | cps.endpoint               | String                        | "pubsub.googleapis.com:443" | The [Pub/Sub endpoint](https://cloud.google.com/pubsub/docs/reference/service_apis_overview#service_endpoints) to use.                                                                                                                                                                                                              |
 | maxBufferSize              | Integer                       | 100                         | The maximum number of messages that can be received for the messages on a topic partition before publishing them to Pub/Sub.                                                                                                                                                                                                        |
-| maxBufferBytes             | Long                          | 10,000,000                  | The maximum number of bytes that can be received for the messages on a topic partition before publishing them to Pub/Sub.                                                                                                                                                                                                           |
+| maxBufferBytes             | Long                          | 9,500,000                   | The maximum number of bytes that can be received for the messages on a topic partition before publishing them to Pub/Sub.                                                                                                                                                                                                           |
 | maxOutstandingRequestBytes | Long                          | Long.MAX_VALUE              | The maximum number of total bytes that can be outstanding (including incomplete and pending batches) before the publisher will block further publishing.                                                                                                                                                                            |
 | maxOutstandingMessages     | Long                          | Long.MAX_VALUE              | The maximum number of messages that can be outstanding (including incomplete and pending batches) before the publisher will block further publishing.                                                                                                                                                                               |
 | maxDelayThresholdMs        | Integer                       | 100                         | The maximum amount of time to wait to reach maxBufferSize or maxBufferBytes before publishing outstanding messages to Pub/Sub.                                                                                                                                                                                                      |