[Feature Request]: Support input variables for agent at `Begin`.

[KevinHuSh]

Is there an existing issue for the same feature request?

• [X] I have checked the existing issues.

Is your feature request related to a problem?

No response

Describe the feature you'd like

Support input variables for agent at Begin. This feature is used for artical generation kind of agent.

Describe implementation you've considered

No response

Documentation, adoption, use case

No response

Additional information

No response