Release v2.12.0 - 2023-09-28

Tag release v2.12.0

References: #112, #133, #134, #135, #136

• Feature - Allow put, update, and delete item options to be passed through to
  the underlying client calls.

• Feature - Add an original_error accessor to Errors::ConditionalWriteFailed
  which contains the Aws::DynamoDB::Errors::ConditionalCheckFailedException
  error. If :return_values_on_condition_check_failure was provided to a put,
  update, or delete item call, this error will contain the item data that failed
  the condition check.

• Issue - Fix default value for String/Numeric Sets to be unset. (#133)

• Feature - Set required Ruby version to >= 2.3 (#134)

• Issue - Run Rubocop on all files. (#135)