Feature/callbacks (#2678)

* wip

* initialize callbacks

* wip

* smtp

* list_service_interfaces

* wip

* wip

* fix domains

* fix hostname handling in NetService

* misc fixes

* getInstalledPackages

* misc fixes

* publish v6 lib

* refactor service effects

* fix import

* fix container runtime

* fix tests

* apply suggestions from review

container-runtime/src/Models/CallbackHolder.ts

@@ -1,12 +1,14 @@
 export class CallbackHolder {
   constructor() {}
-  private root = (Math.random() + 1).toString(36).substring(7)
   private inc = 0
   private callbacks = new Map<number, Function>()
   private newId() {
     return this.inc++
   }
-  addCallback(callback: Function) {
+  addCallback(callback?: Function) {
+    if (!callback) {
+      return
+    }
     const id = this.newId()
     this.callbacks.set(id, callback)
     return id