support ssh configs (aliases, sshCommand and such)

A lot of SSH issues boil down to `.ssh/config` not being used. 
libgit2 added support for using OpenSSH instead of using libssh: https://github.com/libgit2/libgit2/pull/6617. 
currently `git2-rs` does not support building libgit2 with it instead: https://github.com/rust-lang/git2-rs/issues/1028

once that is available we can test whether this fixes such issues.