AssistantAgent.metadata for user/application identity information associated with the agent. #6048

[tongyu0924]

Why are these changes needed?

This PR introduces a metadata field in AssistantAgentConfig, allowing applications to assign and track identity information for agents.
The metadata field is a Dict[str, str] and is included in the configuration for proper serialization.

Related issue number

Closes #6048

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[ekzhu]

Looks good. Just the API docs need to be updated as well.

[tongyu0924]

Looks good. Just the API docs need to be updated as well.

I've modified it, but I'm not sure if it's correct

[ekzhu]

Looks good. Just the API docs need to be updated as well.

I've modified it, but I'm not sure if it's correct

It's not. The api doc is the doc string of AssistantAgent

[tongyu0924]

Looks good. Just the API docs need to be updated as well.

I've modified it, but I'm not sure if it's correct

It's not. The api doc is the doc string of AssistantAgent

I've added the metadata docstring to AssistantAgent — could you help confirm if the wording is correct?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.65%. Comparing base (fc2c997) to head (9e199a3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6057   +/-   ##
=======================================
  Coverage   76.64%   76.65%           
=======================================
  Files         191      191           
  Lines       13220    13222    +2     
=======================================
+ Hits        10133    10135    +2     
  Misses       3087     3087           

Flag	Coverage Δ
unittests	76.65% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[ekzhu]

Please run poe format to fix formatting issues.

[tongyu0924]

Please run poe format to fix formatting issues.

I’ve run poe format and pushed the changes.