[FLINK-29688] Add test to detect changes in DynamoDB model

[dannycranmer]

What is the purpose of the change

Add test to detect changes in DynamoDB model

Brief change log

• Add test to detect changes in DynamoDB model

Verifying this change

Tests pass

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? n/a

[hlteoh37]

LGTM. Just wonder if we should be a little tighter on the contract (e.g. field types). However, approving, since it is more likely that when contract changes, fields are added, rather than modified (for backwards compatibility)