serve workflow templates from custom_nodes (#6193)

* add GET /workflow_templates

* serve workflow templates from custom_nodes

* refactor into custom_node_manager, add test

* remove unused import

* revert changes in folder_paths

* Remove trailing whitespace.

* account for multiple custom_nodes paths

app/custom_node_manager.py

@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+import os
+import folder_paths
+import glob
+from aiohttp import web
+
+class CustomNodeManager:
+    """
+    Placeholder to refactor the custom node management features from ComfyUI-Manager.
+    Currently it only contains the custom workflow templates feature.
+    """
+    def add_routes(self, routes, webapp, loadedModules):     
+
+        @routes.get("/workflow_templates")
+        async def get_workflow_templates(request):
+            """Returns a web response that contains the map of custom_nodes names and their associated workflow templates. The ones without templates are omitted."""
+            files = [
+                file
+                for folder in folder_paths.get_folder_paths("custom_nodes")
+                for file in glob.glob(os.path.join(folder, '*/example_workflows/*.json'))
+            ]
+            workflow_templates_dict = {} # custom_nodes folder name -> example workflow names
+            for file in files:
+                custom_nodes_name = os.path.basename(os.path.dirname(os.path.dirname(file)))
+                workflow_name = os.path.splitext(os.path.basename(file))[0]
+                workflow_templates_dict.setdefault(custom_nodes_name, []).append(workflow_name)
+            return web.json_response(workflow_templates_dict)
+        
+        # Serve workflow templates from custom nodes.
+        for module_name, module_dir in loadedModules:
+            workflows_dir = os.path.join(module_dir, 'example_workflows')
+            if os.path.exists(workflows_dir):
+                webapp.add_routes([web.static('/api/workflow_templates/' + module_name, workflows_dir)])