feat(kv): index utility type (#16910)

* feat(kv): new index type for managing kv indexes

* feat(kv): index verify diff now can produce list of corrupt foreign keys

* fix(testing): refactor kv index tests into testing package and integrate with bolt

* chore(kv): fix go lint error in index

* fix(kv): add test for index walk

* fix(kv): change index cursing strategy to reduce calls to source bkt.Get

* feat(kv): add delete and populate remove dangling foreign keys to index