title: Promql when a PromQL + duration would be firing
body: <p>I was wondering if it's possible to acheive with PromQL:</p>
  <p>Given an promql, and duration produce a graph of when it was active for the duration.
  This is so you could retroactively see when a promQl would have produced alerts.</p>
  <p>I thought doing something like this:</p>
  <pre><code>count_over_time(
     ($PROMQL)[$DUR:15s]
  ) &gt;= ($DUR / 15s)
  </code></pre>
  <p>But it misses this case:
  <a href="https://i.stack.imgur.com/whD1c.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/whD1c.png" alt="" /></a></p>