Different Key/Value Stores must use different namespaces

When one requests a KeyValueStore that doesn't exist to the KeyValueService, it fallbacks to the default one.

However the expectation of the caller is still to see its own key/value store without risk of key collision with what's in the default key/value store.

So we should find a namespacing solution even inside a single key/value store, or use some kind of templating so that unknown key/value stores use the same template as the default.