add callback for getContainerIp (#2851)

* add callback for getContainerIp

* register callback before retrieving info

* version bump; only use backports for linux

core/startos/src/service/effects/mod.rs

@@ -192,6 +192,4 @@ pub fn handler<C: Context>() -> ParentHandler<C> {
             "get-system-smtp",
             from_fn_async(system::get_system_smtp).no_cli(),
         )
-
-    // TODO Callbacks
 }