Add support for changing system message role - this allows using o1-preview and o1-mini models

[faisalil]

Why are these changes needed?

To use the o1-preview and o1-mini models, we cannot send messages with role "system", to deal with this, I allowed controlling the role of the system message via an optional param.

Related issue number

N/A

Checks

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• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[faisalil]

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[faisalil]

I see https://github.com/microsoft/autogen/pull/3530/files just now - happy to close this one if not needed

[jackgerrits]

Thanks for the PR, we're still working on O1 support. Did you want to try out that other PR or provide feedback?

[rysweet]

This PR is against AutoGen 0.2. AutoGen 0.2 has been moved to the 0.2 branch. Please rebase your PR on the 0.2 branch or update it to work with the new AutoGen 0.4 that is now in main.