S3Source extends from FileBatchSource, but doesn't expose FileBatchSource's functionality to allow users to pass filesystem properties.
Added the ability for S3 Batch Source and Sinks to set additional file system properties.
As part of this, also remove the fileSystem property from FileBatchConfig, and make S3BatchConfig extend from FileBatchConfig.
Should be the same for Sink. The actual use-case is that one should be able to read .gz files from S3.