Every shim implementation needs to select a correct publisher topic when posting events, so move it out of Linux-only runc code to the place where other shims can also use it
Otherwise, shims have to copy-paste this code. For example, see runj: 8158e558a3/containerd/shim.go (L144-L172)
Signed-off-by: Marat Radchenko <marat@slonopotamus.org>
