Add option to see reasoning content

[niba]

When you try to use a model with reasoning capability like DeepSeek R1, the chat buffers don't display the reasoning process text. You only see the final answer. Very often, reasoning can be helpful to see how the model processed information in order to get final answer

It is also bad for UX because when you ask something, you need to wait for a long time without any response.

The DeepSeek API returns reasoning_content in addition to content.

https://api-docs.deepseek.com/guides/reasoning_model

[olimorris]

Duplicate of #669

[olimorris]

This has been added in #716