Consolidate design documents

[avishnu]

Description

Project maintainers have decided to maintain the current and future architecture and design documents of the various OpenEBS engines/features in a single location in the current repository. Most of the component and feature design docs are scattered in individual repositories and some of them are missing. This effort is to consolidate all of them into a common location.

Example folder structure: openebs / designs / replicated-pv / mayastor openebs / designs / local-pv / hostpath | lvm | zfs | rawfile