Use HttpClient for POST and DELETE calls

- [Instructor] Using the Angular HTTP Client…post and delete methods…are similar to how you use the GET method.…Let's update the mediaItem service class…to make post and delete calls,…using the HTTP Client service.…For the ad call, we're going…to return a call to http.post.…The post method takes in a URL string…as the first argument, so we set that…to the media item's URL that the mock backend supports.…

The second argument is the body of the post.…The HTTP Client methods support passing different…data types to them, and they will…auto-detect the content type, and handle…setting the content type header.…So we can pass in the media item as is,…and the underlying code will detect it as an object,…and set the content-type header to application/json.…Now we can switch over…to the media-item-form.component.ts file,…and we can refactor the onsubmit method.…

This is already calling the mediaItemservice.add method,…which prepares the observable, but we need to subscribe…to the return of that to kick it off.…So we add .subscribe.…