Handle long log messages correctly on SizedLogger

This is my first “as AWS” commit on moby.

The SizedLogger interface tells logger.Copier that CloudWatch’s upper limit is 262118 bytes. However, moby’s logger package has a few logger wrappers that wrap actual loggers. The wrapper structs didn’t implement SizedLogger. So logger.Copier was chopping long lines by its default upper limit, which is 16KB.

The good news is that awslogs is the only affected logger. The bad news is that SizedLogger was introduced in 2017 for awslogs and hasn’t been used by anybody else since then.