Make node_image_version a settable __init__ param for agent pool models

Per reviewer feedback (FumingZhang), in addition to removing readonly
from _validation, the __init__ methods need to accept node_image_version
as a parameter and assign it instead of hardcoding None. Without this,
the serializer still cannot pass the value through during rollback.

Changes for AgentPool, ManagedClusterAgentPoolProfileProperties, and
ManagedClusterAgentPoolProfile (matching Azure#9742 pattern).
MachineProperties and Snapshot are unchanged (genuinely read-only).

Author: InduSridhar

src/aks-preview/azext_aks_preview/vendored_sdks/azure_mgmt_preview_aks/models/_models_py3.py

@@ -661,6 +661,7 @@ def __init__(  # pylint: disable=too-many-locals
         type_properties_type: Optional[Union[str, "_models.AgentPoolType"]] = None,
         mode: Optional[Union[str, "_models.AgentPoolMode"]] = None,
         orchestrator_version: Optional[str] = None,
+        node_image_version: Optional[str] = None,
         upgrade_strategy: Optional[Union[str, "_models.UpgradeStrategy"]] = None,
         enable_os_disk_full_caching: Optional[bool] = None,
         upgrade_settings: Optional["_models.AgentPoolUpgradeSettings"] = None,
@@ -943,7 +944,7 @@ def __init__(  # pylint: disable=too-many-locals
         self.mode = mode
         self.orchestrator_version = orchestrator_version
         self.current_orchestrator_version: Optional[str] = None
-        self.node_image_version: Optional[str] = None
+        self.node_image_version = node_image_version
         self.upgrade_strategy = upgrade_strategy
         self.enable_os_disk_full_caching = enable_os_disk_full_caching
         self.upgrade_settings = upgrade_settings
@@ -6605,6 +6606,7 @@ def __init__(  # pylint: disable=too-many-locals
         type: Optional[Union[str, "_models.AgentPoolType"]] = None,
         mode: Optional[Union[str, "_models.AgentPoolMode"]] = None,
         orchestrator_version: Optional[str] = None,
+        node_image_version: Optional[str] = None,
         upgrade_strategy: Optional[Union[str, "_models.UpgradeStrategy"]] = None,
         enable_os_disk_full_caching: Optional[bool] = None,
         upgrade_settings: Optional["_models.AgentPoolUpgradeSettings"] = None,
@@ -6887,7 +6889,7 @@ def __init__(  # pylint: disable=too-many-locals
         self.mode = mode
         self.orchestrator_version = orchestrator_version
         self.current_orchestrator_version: Optional[str] = None
-        self.node_image_version: Optional[str] = None
+        self.node_image_version = node_image_version
         self.upgrade_strategy = upgrade_strategy
         self.enable_os_disk_full_caching = enable_os_disk_full_caching
         self.upgrade_settings = upgrade_settings
@@ -7263,6 +7265,7 @@ def __init__(  # pylint: disable=too-many-locals
         type: Optional[Union[str, "_models.AgentPoolType"]] = None,
         mode: Optional[Union[str, "_models.AgentPoolMode"]] = None,
         orchestrator_version: Optional[str] = None,
+        node_image_version: Optional[str] = None,
         upgrade_strategy: Optional[Union[str, "_models.UpgradeStrategy"]] = None,
         enable_os_disk_full_caching: Optional[bool] = None,
         upgrade_settings: Optional["_models.AgentPoolUpgradeSettings"] = None,
@@ -7546,6 +7549,7 @@ def __init__(  # pylint: disable=too-many-locals
             type=type,
             mode=mode,
             orchestrator_version=orchestrator_version,
+            node_image_version=node_image_version,
             upgrade_strategy=upgrade_strategy,
             enable_os_disk_full_caching=enable_os_disk_full_caching,
             upgrade_settings=upgrade_settings,