[Feature]: SFTP Data Source to Support Private Key Authentication

### Feature description

Exports support private key:
<img width="626" height="394" alt="Image" src="https://github.com/user-attachments/assets/1e783518-205a-4790-a192-3a93d99a4a01" />

but not imports:

<img width="665" height="324" alt="Image" src="https://github.com/user-attachments/assets/6e08ea6f-9a2f-452d-a0d4-d9ff8961b723" />