add new option `overwrite_by_pkeys` for DynamoDB `batch_write_item`

[jetjinser]

Describe the feature

like boto3:
https://github.com/boto/boto3/blob/5eaa86735c78be7332fbc340813ba286a629f92b/boto3/dynamodb/table.py#L91
Avoid validation error "Provided list of item keys contains duplicates" when batch write item by auto de-dup.

Use Case

Now I have to manually remove duplicates, but AttributeValue does not implement the Eq, Ord and Hash traits, which complicates the implementation.

Proposed Solution

No response

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

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[ysaito1001]

Thank you for submitting an enhancement request! Since the ability to remove duplicates is not modeled for the input to BatchWriteItem, the requested functionality will need to be implemented as some sort of a high level library (which is why you find it in boto3).