Translate chat and message API docs to English

[CaralHsi]

The chat and message API reference currently exists only in Chinese. This issue is to add English translations.

Files to translate

Translate:

• docs/cn/open_source/open_source_api/chat/chat.md
• docs/cn/open_source/open_source_api/message/feedback.md
• docs/cn/open_source/open_source_api/message/get_message.md
• docs/cn/open_source/open_source_api/message/get_suggestion_queries.md

Place translated files under:

• docs/en/open_source/open_source_api/chat/
• docs/en/open_source/open_source_api/message/

Requirements

• Keep API paths, parameter names, and JSON examples unchanged.
• Translate explanatory text into clear English.
• Preserve Markdown structure.

Acceptance Criteria

• English docs are added for all listed files.
• API examples remain unchanged.
• Markdown renders correctly.