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: libgit2/libgit2#6617.
currently git2-rs does not support building libgit2 with it instead: rust-lang/git2-rs#1028

once that is available we can test whether this fixes such issues.