feat(workload-orchestration): add unstage command for solution versions

Add new `unstage` command to remove staged solution versions from targets. This command:
- Implements the unstage operation following the AAZ pattern
- Supports long-running operations (LRO) with no-wait flag
- Includes command to fetch updated solution version after unstaging
- Adds proper argument validation and resource group support

Example usage:
```
az workload-orchestration target unstage -n myTarget -g myResourceGroup --solution-version-id <arm-id>

Author: tanmay-yerunkar-ms

src/workload-orchestration/azext_workload_orchestration/aaz/latest/workload_orchestration/target/__init__.py

@@ -20,6 +20,7 @@
 from ._update_external_validation_status import *
 from ._show import *
 from ._uninstall import *
+from ._unstage import *
 from ._update import *
 from ._wait import *
 from ._solution_instance_list import *