feat(storage): implement move command

[nhedger]

Note

Disclosure:

• AI assistance was used to implement this feature
• Manual review and testing was done

Description

Closes #604

This PR adds exo storage move (mv) to move objects within a bucket or across buckets without downloading them locally.

The implementation uses server-side copy + delete for regular objects, and multipart server-side copy for large objects. It also preserves object metadata, headers, and ACLs across the move.

A few notes to help review:

• cmd/storage/storage_move.go adds the new CLI command, argument parsing, dry-run / verbose behavior, recursive prefix support, and a --concurrency flag for multipart copy workers
• pkg/storage/sos/move.go adds the storage-layer move implementation for both single-object and recursive moves, including multipart copy + abort-on-failure handling
• pkg/storage/sos/acl.go refactors ACL translation so the same ACL preservation logic can be reused for both CopyObject and CreateMultipartUpload
• pkg/storage/sos/object.go extracts multipart part-size calculation into a shared helper so upload and move use the same dynamic sizing logic and stay under the 10,000-part limit
• pkg/storage/sos/s3api.go, pkg/storage/sos/s3api_mock_test.go, and pkg/storage/sos/move_test.go extend the S3 abstraction and test coverage for HeadObject, multipart copy, abort handling, and configurable concurrency

Open questions

• Should --concurrency remain a user-facing flag for multipart moves? While it can improve large-object move times, higher values may put additional strain on the object storage backend and increase request pressure on the infrastructure.

Checklist

(For exoscale contributors)

• Changelog updated (under Unreleased block, and add the Pull Request #number for each bit you add to the CHANGELOG.md)
• Testing

Testing

• go test ./...
• verified dry-run behavior for single-object moves
• verified same-bucket object moves
• verified cross-bucket object moves
• verified recursive cross-bucket prefix moves
• verified live >5 GiB cross-bucket move path
• verified configurable multipart copy concurrency