title: apply increase over non-existent values replacing them with zero
body: <p>I have an unscheduled batch job that may or may not be triggered multiple times a day. For every invocation, I'm generating a count metric incremented by 1.</p>
  <p>I expected to apply <code>increase()</code> function over 1 day for the metric and see a spike for every invocation of that day.</p>
  <p>However, I noticed increase function doesn't show or extrapolate data for extended missing period (like the period before adding these metrics) and hence the first invocation always makes zero increments.</p>
  <p>I'm trying something like <code>increase(job_invocation_total[1d])</code>.</p>
  <p>I also tried to set the non-existent values as zero with <code>OR on() vector(0)</code> but <code>increase()</code> function didn't allow it.</p>
  <p>Similarly for <code>clamp_min()</code></p>
  <p>I'm pretty sure there must be a standard way of achieving it but unfortunately, I can't think of it.</p>