Refactor documentation structure and update image paths

The documentation has been restructured for better organization. All files under the 'docs' directory have been moved to a new 'privacy-engine' subdirectory. This change also involved updating the paths of several images in the markdown files to reflect their new locations. Additionally, two new index.md files were created under 'privacy-engine' and 'sharded-storage'. The docusaurus configuration file was updated to accommodate these changes.

Author: snjax