Reduce verbose logging when running validation on Flink

The logging in the AWS2 DefaultS3ClientBuilderFactory is extremely verbose when running Beam-on-Flink. For reference, the logged statement "INFO: The AWS S3 Beam extension was included in this build, but the awsRegion flag was not specified. If you don't plan to use S3, then ignore this message." appears in a full run of the Beam Go Flink integration tests 79,970 times. The log statement should be stepped back to being a debug logging statement to make output logs more clear to read.