Part of #1827
Moves `cmd/atelet/internal/ategcs` to `pkg/objectstorage` and renames
the package to `objectstorage`. No code changes besides the package
name, its import path and uses, the tracer name, and comments that named
the old package.
**Why:** the [Platform-Provided Snapshot API
Proposal](https://docs.google.com/document/d/1ac-hY6zsmX4FmtGOt9CXbNFHeluGouyYluer7kX6bto)
moves snapshot transfer out of atelet and ate-api-server into a snapshot
plugin binary that runs as a sidecar. The reference plugin (GCS and S3)
reuses this package's transfer code as is, and so can snapshot plugins
built outside this repository, which is why it goes in `pkg/` rather
than `internal/`.
**Naming:** `objectstorage`, not `objectstore`, because
`internal/objectstore` already exists. That package only lists, copies
and deletes objects for the control plane and is deliberately separate
from this one (see its package comment, updated here). The snapshot
plugin binary imports both.
This PR stands alone and changes no behavior.
**Reviewing:** `git show -M --stat` shows 20 renames as
`{cmd/atelet/internal/ategcs => pkg/objectstorage}/...`. Each changes
only its `package` clause, except:
- `objects.go`: tracer name `ategcs` → `objectstorage`
- `gcscompose_test.go`, `s3bench_test.go`: the `go test
./pkg/objectstorage` path in a comment; `gcscompose_test.go` also
renames its emulator test bucket
The other 4 files:
- `cmd/atelet/{main,main_test,sandbox_assets}.go`: import path and
`ategcs.` → `objectstorage.`, plus one comment in `main_test.go`
- `internal/objectstore/objectstore.go`: package comment now points at
`pkg/objectstorage`
- [x] Tests pass (`make test`, `make verify`)
- [x] Appropriate changes to documentation are included in the PR (none
needed)
