Allow returning thought in the tool call responses

[osdemah]

Why are these changes needed?

Some models (e.g. anthropic models) include a "thought" text message in the tool call responses. This change allows including those messages in the response.

Related issue number

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.

[osdemah]

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

[ekzhu]

@osdemah thanks for the PR.

Due to it's size and the scope of the change -- it is a breaking change, let's have a discussion? Could you create a new issue so we can have a discuss there.

[osdemah]

thanks @ekzhu. created #5192