This adds a Windows Shell Extension that shows overlay icons on folders
that are included in Duplicati backups, similar to how cloud storage
solutions like OneDrive and Google Drive indicate sync status.
The feature includes:
- New API endpoint /api/v1/folderstatus to query backup status of folders
- Windows Shell Icon Overlay handlers for backed up, warning, error and
syncing states
- Client methods in DuplicatiServerClient for the new endpoint
- Registration script for the COM shell extension
Closes#6450
Kenneth Skovhede