Bring back optimization for listing prefixes

[mniewrzal]

Currently, we have some issues with listing large prefixes. In the past (before metabase) we had optimization that was helping with that but we didn't move it to metabase. This optimization is for non-recursive prefix listing.

Optimization was working in a way that if while listing key contained delimiter (/) then the current listing page was dropped and the cursor for the next page was set to prefix<byte of / + 1>.

Old implementation can be found here (see skipPrefix): https://review.dev.storj.io/c/storj/storj/+/4607/3/storage/cockroachkv/ordered_iterator.go

Acceptance Criteria:

• implement optimization
• add test cases if we don't have case that cover non recursive listing of prefix
• write benchmark

[storjBuildBot]

Change https://review.dev.storj.io/c/storj/storj/+/8043 mentions this issue.

[mniewrzal]

All additional optimization can be discussed here https://github.com/storj/team-metainfo/issues/116