fix: extra args not work to disable thinking

[liuyunrui123]

Supports extra_body parameter input to disable thinking

Why are these changes needed?

Allows passing extra_body when creating an openai model client to support the thinking model non-thinking mode of Doubao or Qwen

Related issue number

Closes #6642

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.

[liuyunrui123]

@ekzhu @victordibia Could you help take a look? Thank you.