Expose LLM usage in workflows (#21766)

Co-authored-by: crazywoola <100913391+crazywoola@users.noreply.github.com>

web/app/components/workflow/constants.ts

@@ -480,6 +480,10 @@ export const LLM_OUTPUT_STRUCT: Var[] = [
     variable: 'text',
     type: VarType.string,
   },
+  {
+    variable: 'usage',
+    type: VarType.object,
+  },
 ]
 
 export const KNOWLEDGE_RETRIEVAL_OUTPUT_STRUCT: Var[] = [
@@ -501,6 +505,10 @@ export const QUESTION_CLASSIFIER_OUTPUT_STRUCT = [
     variable: 'class_name',
     type: VarType.string,
   },
+  {
+    variable: 'usage',
+    type: VarType.object,
+  },
 ]
 
 export const HTTP_REQUEST_OUTPUT_STRUCT: Var[] = [
@@ -546,6 +554,10 @@ export const PARAMETER_EXTRACTOR_COMMON_STRUCT: Var[] = [
     variable: '__reason',
     type: VarType.string,
   },
+  {
+    variable: '__usage',
+    type: VarType.object,
+  },
 ]
 
 export const FILE_STRUCT: Var[] = [