Support MAX_BATCH_SIZE env variable

[tjvananne]

The TARGET_S3_MAX_BATCH_SIZE env var only seems to work whenever I declare my own default max_batch_size value in the meltano.yml configuration. This doesn't seem to be the case for other environment variables such as TARGET_S3_APPEND_DATE_TO_FILENAME_GRAIN.

I'm guessing this is also related to how max_batch_size doesn't appear on the meltano hub documentation page or in the meltano config target-s3 set --interactive list.

Is this expected behavior? I'm on Meltano 2.20.0 for... reasons.