Add input_fields and output_fields to make the message more flexible.

[yxjiang]

Is this a Bug or Feature Request?

Feature request

Description

Currently the message by default is expected to have the "input" and "output" fields. This restricted the flexibility.
We want to add two fields, "input_fields", "output_fields", each is a list of Param like config.

When handle the message, we first read those two fields and determine which fields to read.

Environment

• PolyMind version:
• Python version:
• Operating System:

Expected Behavior (Only for bugs)

Actual Behavior (Only for bugs)

Steps to Reproduce (Only for bugs)

1. Step 1
2. Step 2
3. ...

Possible Solution (if you have one)

Screenshots / Logs (If applicable)

Checklist

• I have indicated whether this is a bug or a feature request.
• I have searched for similar issues and didn't find any duplicates.
• I have provided a clear and concise description of the issue.
• I have included the necessary environment details.
• I have outlined the steps to reproduce the issue.
• I have included any relevant logs or screenshots.