feat: add support for custom chat models in configuration

[moritalous]

#40

I made changes to add support for custom chat models in the configuration.

However, I was unable to get it to work as expected with the OpenAI o1-mini model and Claude 3.7 Sonnet (on Bedrock).

Issues encountered: OpenAI o1-mini Encountered the following error:

"Unsupported value: 'messages[0].role' does not support 'developer' with this model."

I believe this issue might be related to the following discussion: https://github.com/langchain-ai/langchain/issues/28895

Claude 3.7 Sonnet Encountered the following error:

"Thinking may not be enabled when tool_choice forces tool use."

It seems that, similar to the special handling for Claude 3.7 Sonnet in grapy.py, with_structured_output does not behave as expected for this model.

Although these models do not work as expected at this time, I believe the changes themselves are valuable, so I am submitting this PR.

Let me know if any adjustments are needed. Thanks!