### What problem does this PR solve?

Unified API response json schema

### Type of change

- [x] Refactoring

### What problem does this PR solve?

Modify the response of metadata in Dify retrieval api

resolve   #2914

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

### What problem does this PR solve?

Turn resource to plural form

### Type of change
- [x] Refactoring

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

### What problem does this PR solve?

Turn resource to plural form

### Type of change

- [x] Refactoring

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

### What problem does this PR solve?

#2687

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._
Fixes #2731 
### Type of change

- [x] New Feature (non-breaking change which adds functionality)