Dump repo partition and _all_ partitions in `lakefs kv dump`

(Discovered in #9768)

Support dumping:

- [ ] *All* partitions.

  `lakefs kv dump` cannot currently dump all partitions - only the 3 specific partitions that it knows about.  Add a mode that to dump everything.
- [ ] The partition of a give repo.

  A single `kv.Get` would give the name of the partition of the repository.  Now dump that.

