Added ability to specify 'role' field for select speaker messages for Group Chats (Replaces PR #2167) (#2199)

* Re-commit of code from PR (#2167) addressing #1861, due to wrong basing

* Update website/docs/topics/non-openai-models/best-tips-for-nonopenai-models.md

Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>

* Removed unnecessary notebook images

* Update conversation-patterns.ipynb

Updated to include note about being applicable when auto.

* Updated to include checks that the role is not blank/None. Added tests.

* Changed try-except to use pytest

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Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>