We had `gitlab-shell-authorized-keys-check` and
`gitlab-shell-authorized-principals-check` as symlinks to
`gitlab-shell` before.

We determine the `Command` and `CommandArgs` that we build based
on the `Name` of the `Executable`. We also use that to know which
fallback ruby executable should we fallback to. We use
`os.Executable()` to do that.

`os.Executable()` behaves differently depending on OS. It may
return the symlink or the target's name. That can result to a
buggy behavior.

The fix is to create binaries for each instead of using a symlink.
That way we don't need to rely on `os.Executable()` to get the name.
We pass the `Name` of the executable instead.