[Iterator] Implement Backend for Iterator step (#14145)

Manually tested by starting to implement the frontend:
- loopStepIds contains a create record action that takes one item at a
time
- items to iterate are a list of string that will be used as record
title


https://github.com/user-attachments/assets/728310d9-4728-422f-a324-3783da24e517

packages/twenty-server/src/modules/workflow/workflow-builder/workflow-schema/workflow-schema.workspace-service.ts

@@ -76,6 +76,15 @@ export class WorkflowSchemaWorkspaceService {
           formFieldMetadataItems: step.settings.input,
           workspaceId,
         });
+      case WorkflowActionType.ITERATOR: {
+        return {
+          nextItemToProcess: {
+            isLeaf: true,
+            type: 'unknown',
+            value: generateFakeValue('unknown'),
+          },
+        };
+      }
       case WorkflowActionType.CODE: // StepOutput schema is computed on serverlessFunction draft execution
       default:
         return {};

packages/twenty-server/src/modules/workflow/workflow-builder/workflow-version-step/workflow-version-step.workspace-service.ts

@@ -654,6 +654,20 @@ export class WorkflowVersionStepWorkspaceService {
           },
         };
       }
+      case WorkflowActionType.ITERATOR: {
+        return {
+          ...baseStep,
+          name: 'Iterator',
+          type: WorkflowActionType.ITERATOR,
+          settings: {
+            ...BASE_STEP_DEFINITION,
+            input: {
+              items: [],
+              initialLoopStepIds: [],
+            },
+          },
+        };
+      }
       default:
         throw new WorkflowVersionStepException(
           `WorkflowActionType '${type}' unknown`,