Refa: refactor prompts into markdown-style structure using Jinja2 (#8667)

### What problem does this PR solve?

Refactor prompts into markdown-style structure using Jinja2.

### Type of change

- [x] Refactoring

rag/prompts/question_prompt.md

@@ -0,0 +1,19 @@
+## Role
+You are a text analyzer.
+
+## Task
+Propose {{ topn }} questions about a given piece of text content.
+
+## Requirements
+- Understand and summarize the text content, and propose the top {{ topn }} important questions.
+- The questions SHOULD NOT have overlapping meanings.
+- The questions SHOULD cover the main content of the text as much as possible.
+- The questions MUST be in the same language as the given piece of text content.
+- One question per line.
+- Output questions ONLY.
+
+---
+
+## Text Content
+{{ content }}
+