title: Pyspark to_timestamp with timezone
body: <p>I am trying to convert datetime strings with timezone to timestamp using to_timestamp.</p>
  <p>Sample dataframe:</p>
  <pre><code>df = spark.createDataFrame([(&quot;a&quot;, '2020-09-08 14:00:00.917+02:00'), 
                              (&quot;b&quot;, '2020-09-08 14:00:00.900+01:00')], 
                             [&quot;Col1&quot;, &quot;date_time&quot;])
  </code></pre>
  <p>My attempt (with timezone specifier Z):</p>
  <pre><code>df = df.withColumn(&quot;timestamp&quot;,f.to_timestamp(df.date_time, &quot;yyyy-MM-dd HH:mm:ss.SSSZ&quot;))
  df.select('timestamp').show()
  </code></pre>
  <p>Actual result:</p>
  <pre><code>    +---------+
      |timestamp|
      +---------+
      |     null|
      |     null|
      +---------+
  </code></pre>
  <p>Wanted result (where timestamp is of type timestamp):</p>
  <pre><code>+-------------------------+
  |                timestamp|
  +-------------------------+
  |2020-09-08 14:00:00+02:00|
  |2020-09-08 14:00:00+01:00|
  +-------------------------+
  </code></pre>
  <p>I have tried many other versions of format as well, but I cannot seem to find the right one.</p>