Clarify PVCs use selective backup in Goals section

Updated Goals section to explicitly state that PVCs are an exception to the
"Full Backup, Selective Restore" pattern.

Clarification:
- CRs, Secrets, ConfigMaps: Full Backup, Selective Restore
- PVCs (exception): Selective Backup, Selective Restore
  - Reason: Storage/performance concerns (large data volumes, snapshot costs)
  - Only PVCs with openstack.org/backup="true" are backed up
  - Only PVCs with openstack.org/backup-restore="true" are restored

This makes the Goals section accurate and prevents confusion about the
backup strategy for different resource types.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: stuggi

docs/dev/backup-restore-webhook-design.md

@@ -6,9 +6,10 @@ This document describes a webhook-based approach to backup and restore for OpenS
 
 ## Goals
 
-1. **Full Backup, Selective Restore**:
+1. **Full Backup, Selective Restore** (for CRs, Secrets, ConfigMaps):
    - Backup: All user resources (Secrets, ConfigMaps, CRs) - complete snapshot
    - Restore: Only webhook-labeled resources - automatic filtering
+   - **Exception - PVCs**: Selective backup AND selective restore (only labeled PVCs backed up/restored due to storage/performance concerns)
 2. **Dynamic Resource Discovery**: No hardcoded lists - CRD annotations declare what needs restore
 3. **Declarative Restore Order**: Restore order defined in CRD annotations, not in code
 4. **Operator-Managed Exclusion**: Operators recreate their own resources (not restored from backup)