Add warning logs for manifests, siblings, bytes and history

Add three kinks of warning logs for potentially bloated manifests.
Original issue is #882.

- many siblings
- large size
- long history ({UUID, M} pairs)

Each has default value and enabled, but has kill switch `disabled`.
This `<Bucket>/<Key>` format is confusing to me. How about format like `(<Bucket>, <Key>)`, separated by space?