The menu doesn't update if a new sub section is added after rendering has already completed

[alexandrevryghem]

Describe the bug
When you add a new subsection to a navbar section that previously didn't have any subsections yet, and that the component has already been rendered, the new subsection(s) don't appear.

To Reproduce
Steps to reproduce the behavior:

1. Add the following code to your HomeNewsComponent:

ngOnInit(): void {
  this.menuService.addSection(MenuID.PUBLIC, Object.assign({
    id: 'test',
    parentID: 'browse_global_communities_and_collections',
    active: false,
    visible: true,
    model: {
      type: MenuItemType.LINK,
      text: 'test',
      link: '/test',
    } as LinkMenuItemModel,
  }, {
    shouldPersistOnRouteChange: true,
  }));
}

2. Go to a random page (except for home, for example /statistics) and refresh the page
3. The Communities & Collections should have no subsection yet
4. Navigate to the home page using the breadcrumbs
5. The subsection is not visible underneath Communities & Collections

Expected behavior
When you add a new subsection to a section that previously didn't have any subsections yet, the component should be updated, and the subsections should be automatically added.