Adds the sharded bucket middleware, which allows for splitting objects
across multiple backend buckets for a given virtual bucket. The
middleware should be configured as:
s3proxy.sharded-blobstore.<bucket name>.shards=<number of shards>
s3proxy.sharded-blobstore.<bucket name>.prefix=<prefix>.
All shards are named <prefix>-<index>, where index is an
integer from 0 to <number of shards> - 1. If the <prefix> is not
supplied, the <bucket name> is used as the prefix.
Listing the virtual bucket and multipart uploads are not supported. When
listing all containers, the shards are elided from the result.
Fixes#325Fixes#351