title: Convert PySpark dataframe column from list to string
body: <p>I have this PySpark dataframe</p>
  
  <pre><code>+-----------+--------------------+
  |uuid       |   test_123         |    
  +-----------+--------------------+
  |      1    |[test, test2, test3]|
  |      2    |[test4, test, test6]|
  |      3    |[test6, test9, t55o]|
  </code></pre>
  
  <p>and I want to convert the column <code>test_123</code> to be like this:</p>
  
  <pre><code>+-----------+--------------------+
  |uuid       |   test_123         |    
  +-----------+--------------------+
  |      1    |"test,test2,test3"  |
  |      2    |"test4,test,test6"  |
  |      3    |"test6,test9,t55o"  |
  </code></pre>
  
  <p>so from list to be string.</p>
  
  <p>how can I do it with PySpark? </p>