Feature request: (OSS) have CLI / UI report bucket storage usage

__Proposal:__
It would be great if there was a way, using the UI and/or the `influx` CLI tool, to have the bucket list report the total storage space being used up by the bucket. I can't see anything obvious right now other than what is in the `/metrics` endpoint, which is not easy-to-access or user-friendly.

__Current behavior:__
No obvious way to find out storage usage of a bucket from the existing user interfaces. Instead, have to look up the bucket ID, then go to the shell and measure storage with `du` (or vice-versa, one might find which bucket ID is happening to be growing excessively using `du`, and then do the exercise of reverse-mapping the bucket ID to a bucket name).

Start with the `/metrics` endpoint and the existing bucket-list entry points in the `influx` CLI and UI; trace how bucket IDs and storage metrics are currently exposed. Clarify whether both interfaces are in scope, then verify that the selected interface reports each bucket's total storage usage without requiring shell access or manual ID mapping.

Written by the indexing model from the issue text.