The s3 and rclone tiered-storage backends were registered via blank imports
in weed/storage (volume_tier.go and volume_info/volume_info.go). That forced
every library consumer of weed/storage -- weed/shell, and through it external
tools -- to link aws-sdk-go and, under the rclone build tag, the full rclone
backend set and its cloud-storage SDKs, even though those consumers never tier
volumes.
Move the registrations into a new weed/storage/backend/all aggregator and
blank-import it once from weed/command, the binary's composition root. The weed
binary still registers both backends; weed/storage and its library consumers no
longer pull the backend SDKs into their dependency graph.
Chris Lu