[Bug][KafkaSource]Fix the default value of commit_on_checkpoint.

[lightzhao]

Fix the default value of commit_on_checkpoint,it is different from the default value described in the document, and the modification is consistent.

Purpose of this pull request

Check list

• Code changed are covered with tests, or it does not need tests for reason:
• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/incubator-seatunnel/tree/dev/docs
• If you are contributing the connector code, please check that the following files are updated:
  1. Update change log that in connector document. For more details you can refer to connector-v2
  2. Update plugin-mapping.properties and add new connector information in it
  3. Update the pom file of seatunnel-dist

[EricJoy2048]

The default value need get from the COMMIT_ON_CHECKPOINT.

[lightzhao]

The default value is from the parameter 'commit_on_checkpoint', but if the user does not set it, the default value of CommitOnCheckpoint of ConsumerMetadata will be taken, and its default value is false.

[EricJoy2048]

We use COMMIT_ON_CHECKPOINT to define the default value.

    public static final Option<Boolean> COMMIT_ON_CHECKPOINT = Options.key("commit_on_checkpoint")
            .booleanType()
            .defaultValue(true)
            .withDescription("If true the consumer's offset will be periodically committed in the background.");

So, I think if user does not set it in config file, you need get the default value from COMMIT_ON_CHECKPOINT.defaultValue(). Otherwise, the defaultValue in Option will lose its meaning.

[lightzhao]

ok, you're right. It's been changed.

need update code

[EricJoy2048]

LGTM

[TaoZex]

LGTM

[lightzhao]

@EricJoy2048 please merge, thanks.

[ic4y]

+1