### 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._

### Type of change

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

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Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

### What problem does this PR solve?

API: Adds the feature of uploading document.

### Type of change

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