title: Subscribe to final observable after all observable completed?
body: <p>I have this logic here, which creates many observable and executes a call back after each of them is done.</p>
  <pre><code>from(rows).pipe(
      concatMap(row =&gt; this.uploadItem(row))
  ).subscribe(response =&gt; {
      this.currentRowNode.data.uploadStatus = UploadStatus.Success;
      this.currentRowNode.data.cmsRowId = response.responsePayload.cmsRowId
      this.currentRowNode.setData(this.currentRowNode.data);
  });
  
  currentRowNode: RowNode;
  uploadItem(rowNode: RowNode): Observable&lt;any&gt; {
      this.currentRowNode = rowNode;
      rowNode.data.uploadStatus = UploadStatus.Uploading;
      rowNode.updateData(rowNode.data);
      return this.importService.uploadItem(rowNode.data)
   }
  </code></pre>
  <p>My issue here is that I'd like to be able to subscribe to something that would tell me <code>uploadItem</code> has been called for each of the <code>rows</code></p>
  <p>Where would that go ?</p>