Investigate allowing SFTP to use an SSH key

[Lansatac]

It would be nice to operate on servers that are configured to not use username authentication.

[chapinb]

This is possible using the same SFTP client that we have, as noted here:

https://csharp.hotexamples.com/examples/Renci.SshNet/SftpClient/-/php-sftpclient-class-examples.html#0xfd2128cea7c5fb03421cea900fed6312fc4b8f6c77cf4bdb620fa253ae2c400c-33,,39,

We could modify this section to use a similar conditional to check for a key then default to a password here:

CyLR/CyLR/src/Program.cs

Line 325 in f76f19f

private static SftpClient CreateSftpClient(Arguments arguments)