Support new openssh format

[jerrywdlee]

In SFTP mode, when I using key like:

-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAAB
.....
X4UnoLYAsrbcj+IftnAAAAGGplcnJ5bGV
-----END OPENSSH PRIVATE KEY-----

I cannot access to the remote server.

But when using key like:

-----BEGIN RSA PRIVATE KEY-----
MIIEpAIBAAKCAQEAyNSIGWfF2IKoLF9eg611rspDdl0K76
....
rRvVNVWz8x9W9VCmfZgI8rcIfVnbnarp+LAxMXRzsx5+jRaO/7Dy6Q==
-----END RSA PRIVATE KEY-----

I can access to the server.

Is vscode-remote-workspace not support new OpenSSH key yet?