database retrieve api and chat-messages api response doc_metadata

[yuhaowin]

Self Checks

• [x] I have searched for existing issues search for existing issues, including closed ones.
• [x] I confirm that I am using English to submit this report (我已阅读并同意 Language Policy).
• [x] [FOR CHINESE USERS] 请务必使用英文提交 Issue，否则会被关闭。谢谢！:）
• [x] Please do not modify this template :) and fill in all the required fields.

1. Is this request related to a challenge you're experiencing? Tell me about your story.

It is expected that the API can return doc_metadata, which can facilitate the acquisition of the original source of the referenced data, such as url, etc.

2. Additional context or comments

No response

3. Can you help us with this feature?

• [x] I am interested in contributing to this feature.