### What problem does this PR solve?
Improve file management. #10287.
Passed tests:
1. Create folder `A` and `B`.
2. Upload a file inside `A`, called `file`.
3. Create a KB, called `K`.
3. Link `file` to `K`.
4. Parse `file` inside of `K`. (OK)
5. Move `file` from `A` to `B`.
6. Parse `file` inside of `K`. (OK)
7. Move `file` from `B` to `A`.
8. Parse `file` inside of `K`. (OK)
9. Move entire folder `A` into `B`. (B -> A -> file)
10. Parse `file` inside of `K`. (OK)
11. Delete folder `B`.
12. All clear. (There is no document inside of `K`)
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
86b254d214