backups: Add component for backup/restore
This patch introduces a backup component that handles backup/restore operations which leads to:
- Cleanup of module level API for 'backup', 'backup_pre', 'backup_post', 'restore_pre' and 'restore_post'.
- Cleanup of manifest importing and associated pylint warnings.
- Cleanup of backup API implementation. Specifically dropping BackupApp in favour of the new backup component.
- Consistency for backup/restore with component approach.