fix: SocietyOfMindAgent should save its response into context

[dason8]

Why are these changes needed?

Currently SocietyOfMindAgent doesn't save its own response message into context, so in a multi round chat scenario, when this SocietyOfMindAgent is picked by upstream orchestrator (e.g. another GroupChat), its last response message shows in neither task messages nor inner context. This results in message lose. Then its inner team won't get same context as other agents in the upper team.

Related issue number

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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.77%. Comparing base (892492f) to head (7848659).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6659      +/-   ##
==========================================
- Coverage   79.78%   79.77%   -0.01%     
==========================================
  Files         228      228              
  Lines       17054    17057       +3     
==========================================
+ Hits        13606    13608       +2     
- Misses       3448     3449       +1     

Flag	Coverage Δ
unittests	79.77% <100.00%> (-0.01%)	⬇️

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[dason8]

@microsoft-github-policy-service agree company="Microsoft"

[dason8]

@ekzhu please have a review.
While I was using this SocietyOfMindAgent, I found the inner team couldn't get its last response (or a summarized version by this SocietyOfMindAgent), which not meet my expection. maybe this is bug.