Support Include directive when reading from OpenSSH config

[cyberduck]

@dkocher created the issue

[partomatl]

This prevents the use of 1Password's SSH Bookmarks for automatic host/key matching: https://developer.1password.com/docs/ssh/bookmarks/#use-the-configuration-file

It relies on including the 1Password-generated file in ~/.ssh/config:

Include ~/.ssh/1Password/config