[FLINK-36296][Connectors/DynamoDB] Add support for incremental shard discovery for DynamoDB Streams Source

[gguptp]

Purpose of the change

DynamoDB has launched a new shard filter API in DescribeStream to discover child shards of a parent shard in AWS SDK 2.32.0. This PR adds support for this new feature.

Verifying this change

Please make sure both new and modified tests in this PR follows the conventions defined in our code quality guide: https://flink.apache.org/contributing/code-style-and-quality-common.html#testing

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

• Added unit tests
• Manually verified by running the dynamodb connector on a local Flink cluster

Significant changes

(Please check any boxes [x] if the answer is "yes". You can first publish the PR and check them afterwards, for convenience.)

• [ x ] Dependencies have been added or upgraded
• Public API has been changed (Public API is any class annotated with @Public(Evolving))
• [ x ] Serializers have been changed
• [ x ] New feature has been introduced
  • If yes, how is this documented? (not applicable / docs / JavaDocs / not documented)