Source file: SSH key authentication via SFTP

## Tell us about the problem you're trying to solve
I just deployed Airbyte and tested a CSV file transfer (from a HTTPS to local storage) and it works nicely. I'm now trying to use CSV File as a Source using SFTP, from a web server hosted on SiteGround. I'm able to connect to SiteGround via SFTP using FileZilla client, https://www.siteground.com/kb/how_to_establish_sftp_connection_to_hosting_with_filezilla/
It requires storing the private key of the server. In Airbyte, I don't see an option to use the SSH private key on the UI. Per @marcosmarxm, this feature is not yet available, and may be requested here.

## Describe the solution you’d like
To have the ability to transfer files via SFTP as a Source, using SSH key file support (not just password authentication, as this is not always available).

Thank you Airbyte team!!