Add Update Manager for automated Part-DB updates

This feature adds a comprehensive Update Manager similar to Mainsail's
update system, allowing administrators to update Part-DB directly from
the web interface.

Features:
- Web UI at /admin/update-manager showing current and available versions
- Support for Git-based installations with automatic update execution
- Maintenance mode during updates to prevent user access
- Automatic database backup before updates
- Git rollback points for recovery (tags created before each update)
- Progress tracking with real-time status updates
- Update history and log viewing
- Downgrade support with appropriate UI messaging
- CLI command `php bin/console partdb:update` for server-side updates

New files:
- UpdateManagerController: Handles all web UI routes
- UpdateCommand: CLI command for running updates
- UpdateExecutor: Core update execution logic with safety mechanisms
- UpdateChecker: GitHub API integration for version checking
- InstallationTypeDetector: Detects installation type (Git/Docker/ZIP)
- MaintenanceModeSubscriber: Blocks user access during maintenance
- UpdateExtension: Twig functions for update notifications

UI improvements:
- Update notification in navbar for admins when update available
- Confirmation dialogs for update/downgrade actions
- Downgrade-specific text throughout the interface
- Progress page with auto-refresh

config/permissions.yaml

@@ -297,6 +297,10 @@ perms: # Here comes a list with all Permission names (they have a perm_[name] co
       show_updates:
         label: "perm.system.show_available_updates"
         apiTokenRole: ROLE_API_ADMIN
+      manage_updates:
+        label: "perm.system.manage_updates"
+        alsoSet: ['show_updates', 'server_infos']
+        apiTokenRole: ROLE_API_ADMIN
 
 
   attachments: