Remove max_number_of_messages for SQS+S3-based inputs

[strawgate]

With elastic/beats#40699 the max_number_of_messages setting is now ignored for SQS inputs as of 8.15. It is still exposed in integration settings. It is still relevant for <8.15.

The new setting is number_of_workers, which the SQS-based input shares with the S3 bucket polling input in integration settings.

Unfortunately, the default value for number_of_workers is just 1. Users using an SQS-based S3 input upgrading to 8.15 agents will find that they've gone from having five workers (or whatever number they had customized it to) for processing objects to just a single worker processing objects.

We should consider one or more of the following:

1. Using the max_number_of_messages setting for the number_of_workers value if queue_url is present to maintain backwards compatibility while indicating that the setting will be removed in a future version.
2. Indicating that max_number_of_messages is no longer applicable for 8.15 and to use number_of_workers when using an SQS queue
3. Bumping the number_of_workers default value to 5