NbSidebar Events not firing in responsive mode

### Issue type

**I'm submitting a ...** (check one with "x")

* [x] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**
If you have a sidebar with responsive set on it and suscribe to the onCollapse and/or the onToggle Observables there are no events fire when you resize the window and the sidebar collapses itself.

**Expected behavior:**
The proper events fire when the sidebar collapses itself from the responsive behavior.

**Steps to reproduce:**

**Related code:**
``

```
public ngOnInit(): void {
this.sidebarService.onToggle().subscribe((value) => {
this.isSidebarExpanded = !this.isSidebarExpanded;
console.log('toggle');
});

this.sidebarService.onCollapse().subscribe((value) => {
this.isSidebarExpanded = false;
console.log('collapsed');
})

}

```