feat(nodes,ui): add detection of custom nodes

Custom nodes have a new attribute `node_pack` indicating the node pack they came from.

- This is displayed in the UI in the icon icon tooltip.
- If a workflow is loaded and a node is unavailable, its node pack will be displayed (if it is known).
- If a workflow is migrated from v1 to v2, and the node is unknown, it falls back to "Unknown". If the missing node pack is installed and the node is updated, the node pack will be updated as expected.

invokeai/app/invocations/custom_nodes/init.py

@@ -6,6 +6,7 @@ import sys
 from importlib.util import module_from_spec, spec_from_file_location
 from pathlib import Path
 
+from invokeai.app.invocations.baseinvocation import CUSTOM_NODE_PACK_SUFFIX
 from invokeai.backend.util.logging import InvokeAILogger
 
 logger = InvokeAILogger.get_logger()
@@ -32,8 +33,8 @@ for d in Path(__file__).parent.iterdir():
     if module_name in globals():
         continue
 
-    # we have a legit module to import
-    spec = spec_from_file_location(module_name, init.absolute())
+    # load the module, appending adding a suffix to identify it as a custom node pack
+    spec = spec_from_file_location(f"{module_name}{CUSTOM_NODE_PACK_SUFFIX}", init.absolute())
 
     if spec is None or spec.loader is None:
         logger.warn(f"Could not load {init}")