Add findAllInRange function in the storage layer

Summary:
In preparation of the support for ranged queries.

Notes:

Since they are pretty similar, it could be nice to refactor scan and findAllInRange to use common 3rd function

Test Plan: This is tested in storagetest.cpp

Reviewers: cmollekopf

Tags: Sink

Differential Revision: https://phabricator.kde.org/D13066