title: How to upload a file to directory in yii2?
body: <p>i have an ActiveForm, and i want to add a field where the user can upload their photos.
  the problem is that i don't have an attribute for the image in the users table and every 
  input field in 'yii' expects a model and an attribute as follows.</p>
  
  <pre><code>&lt;?= $form-&gt;field($model, 'attribute')-&gt;input($platforms) ?&gt;
  </code></pre>
  
  <p>i don't want to assign the image to any record nor i want to insert in in the database, i want it to be uploaded to a specific folder.</p>
  
  <p>i have also checked the library kartik wrote, but also requires an attribute field.</p>