title: count of subquery in doctrine - querybuilder
body: <p>I have simple query:</p>
  
  <pre><code>$this-&gt;qb-&gt;select('l.value')
          -&gt;addSelect('count(l) AS cnt')
          -&gt;addSelect('hour(l.time) AS date_hour')
          -&gt;from(Logs::class, 'l')
          -&gt;where('l.header = :header')
          -&gt;groupBy('l.value')
          -&gt;addGroupBy('date_hour')
          -&gt;setParameter('header', 'someheader')
  </code></pre>
  
  <p>This code select 3 columns have one condition and two groupBy.</p>
  
  <p>I want get <strong>records count</strong> of this query. Of course I dont want to download all records and check size of downloaded data. </p>
  
  <p><strong>Question:</strong> 
  How to rebuild this query and get result from db as singleScalarValue()?</p>