Integrate S3 storage source extension logging with WiredTiger verbose messaging

The S3 extension will generate logs of various kinds, namely, failures, warnings, and other levels. These logs will come from the extension itself and from the AWS SDK library's logging. We want to feed these into WiredTiger's logging streams, such that there is a best effort in mapping the levels to WiredTigers levels.

This ticket will explore the best means to do that. Apart from writing the logging code, some way to test that the logs and levels work as expected will need to be devised.