title: Upload adapter is not defined Issue with Image uploading in ckeditor5-angular
body: <p>This question may have already answers but none of them is Angular specific.
  Here are some of them</p>
  
  <ul>
  <li><a href="https://stackoverflow.com/q/49264105/4887891">CKEditor 5 and Image Button </a></li>
  <li><a href="https://stackoverflow.com/q/46765197/4887891">How to enable image upload support in CKEditor 5?</a></li>
  <li><a href="https://stackoverflow.com/q/51984752/4887891">Insert image to CKeditor
  </a></li>
  </ul>
  
  <p>I am using Angular 5 and following <a href="https://www.npmjs.com/package/@ckeditor/ckeditor5-angular" rel="noreferrer">this</a> documentation to implement ckeditor5-angular. </p>
  
  <p>But I am having issue with image uploading, when I try uploading image it says in the browser console.</p>
  
  <blockquote>
    <p>filerepository-no-upload-adapter: Upload adapter is not defined. Read more: <a href="https://docs.ckeditor.com/ckeditor5/latest/framework/guides/support/error-codes.html#error-filerepository-no-upload-adapter" rel="noreferrer">https://docs.ckeditor.com/ckeditor5/latest/framework/guides/support/error-codes.html#error-filerepository-no-upload-adapter</a></p>
  </blockquote>
  
  <p>I have tried searching for this issue and was able to find a lot of solutions, but literally I couldn't understand a single of them because they were not Angular specific. </p>
  
  <p>Please help how can I upload image.</p>