support ssh configs (aliases, sshCommand and such)

[extrawurst]

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.