fix(storage): add extra debug logging for GCS stat and blob transfer service

Context

While testing imports manually on pre, we encountered the following import failures: pre importing tagged manifests: pre importing manifest: pre importing manifest: transferring blob with digest sha256:45b430cac0361a5a1cc5401c3b9086a860fa349f46ea422c00570340cbbd705f: %!v(PANIC=Error method: runtime error: invalid memory address or nil pointer dereference)

This MR seeks to increase the logging visibility temporarily to help resolve this issue.