Support Google Cloud Storage nearline

Google announced a new storage offering for GCS, nearline support:

https://cloud.google.com/storage/docs/nearline-storage

This has some performance tradeoffs:

Note: You should expect 4 MB/s of throughput per TB of data stored as Nearline Storage. This throughput scales linearly with increased storage consumption. For example, storing 3 TB of data would guarantee 12 MB/s of throughput, while storing 100 TB of data would provide users with 400 MB/s of throughput.