[Feature]: Support passing user-defined fields in `SubAgentTool`

[AlbumenJ]

Problem Description
Currently, SubAgentTool is implemented solely based on conversation history. Consequently, users cannot pass external parameters (e.g., userId) to the sub-agent securely or accurately.

Proposed Solution
We need to design a mechanism that allows users to define and pass specific fields to the SubAgentTool explicitly.

[ShenJunkun]

@AlbumenJ I'm interested in this issue. Please assign it to me.

[ShenJunkun]

@AlbumenJ
I have gone through the code in SubAgentTool.java, and I have a few questions I’d like to ask:

• How will these external parameters be used? For example, if a userId is passed to a sub-agent, how specifically will the sub-agent utilize it?
• How should I handle these external parameters? Should I concatenate them with the userMsg?

  agentscope-java/agentscope-core/src/main/java/io/agentscope/core/tool/subagent/SubAgentTool.java

  Lines 152 to 157 in b317f03

  	// Build user message
  	Msg userMsg =
  	Msg.builder()
  	.role(MsgRole.USER)
  	.content(TextBlock.builder().text(message).build())
  	.build();

[AlbumenJ]

It's better to define a custom Msg. We also support call(List<Msg>).
The Msg can contain custom parameters. I would like to extract this key as a Tool parameter, which can be injected either by the model or via the ToolExecutionContext.

[Vinke2]

I'm also stuck here now, is there any progress?