Add iteration for agent. (#4258)

### What problem does this PR solve?

#4242
### Type of change

- [x] New Feature (non-breaking change which adds functionality)

agent/component/__init__.py

@@ -32,6 +32,8 @@ from .crawler import Crawler, CrawlerParam
 from .invoke import Invoke, InvokeParam
 from .template import Template, TemplateParam
 from .email import Email, EmailParam
+from .iteration import Iteration, IterationParam
+from .iterationitem import IterationItem, IterationItemParam
 
 
 
@@ -103,6 +105,10 @@ __all__ = [
     "CrawlerParam",
     "Invoke",
     "InvokeParam",
+    "Iteration",
+    "IterationParam",
+    "IterationItem",
+    "IterationItemParam",
     "Template",
     "TemplateParam",
     "Email",