[code_review] Add CoT explanations to examples of comments

See http://arxiv.org/pdf/2311.16452, it should improve quality.

We can also use the generated CoT explanations to help people understand the generated comments and verify if they are correct.

The generated CoT explanations could also be used by the LLM as judge to validate the comments (#4584).

Should CoT explanations also contain tool usage? In some cases it might be necessary to use a tool in order to generate a comment, if no CoT contains tool usage, maybe the model will never use tools.