Added ability to specify 'role' field for select speaker messages for Group Chats (Replaces PR #2167)

[marklysze]

Note: This replaces #2167 due to it being based on an older version of main.

Why are these changes needed?

As per feature request #1861 ("[Feature Request]: Allowing user to specify the "role" field for select speaker messages"), this PR includes changes to the GroupChat constructor to allow the user to specify the role for the select speaker messages. This addresses the issue of role names when using Mistral through Mistral.AI's API.

Changes:

• Added role_for_select_speaker_messages to GroupChat constructor in groupchat.py
• Added @ekzhu's Mistral.AI notebook to documentation under Non-OpenAI models section
• Added @ekzhu's updates to the Using Non-OpenAI about page
• Added a Tips for Non-OpenAI models page to documentation (should be a basis for future tips)
• Added a sub-section on the Conversation Patterns tutorial explaining the new attribute and provided an example

Related issue number

Addresses #1861

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation 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]

Unit tests to check if the select speaker messages are indeed following the role specified

[marklysze]

Unit tests to check if the select speaker messages are indeed following the role specified

Okay, I'll add to tests

[marklysze]

Unit tests to check if the select speaker messages are indeed following the role specified

I've added a test for this. I've also updated groupchat.py (sorry @jackgerrits!) to include a check that role_for_select_speaker_messages isn't blank or None.

[marklysze]

I've updated the tests to use pytest instead of try-except (as per my other PR).

[sonichi]

Could you please fix the conflicts? Thanks.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 49.73%. Comparing base (989c182) to head (0a2b4d7).

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2199       +/-   ##
===========================================
+ Coverage   37.83%   49.73%   +11.90%     
===========================================
  Files          77       77               
  Lines        7766     7769        +3     
  Branches     1663     1801      +138     
===========================================
+ Hits         2938     3864      +926     
+ Misses       4579     3583      -996     
- Partials      249      322       +73     

Flag	Coverage Δ
unittest	14.36% <33.33%> (?)
unittests	48.66% <100.00%> (+10.84%)	⬆️

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