Fix recent change to Batch operator's retry_strategy

[ferruzzi]

Should fix #35789

"attempts" is a required field if retry_strategy is used. By doing it this way, we can also verify that a user-provided retry_strategy has a valid attempts value.

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[ferruzzi]

One possible point to discuss: The 'attempts' value must be between 1 and 10. The API will return a ClientError if a value outside that range is provided. Do we want to catch that at init or just let the API handle it at runtime? I'm tempted to let the API handle it so we don't have to chase it if/when they make a change to the available range.