title: Jenkins:Pipeline optional manual stage, that does not block any agent
body: <p>Imagine a <em>multibranch</em> pipeline, that has stages <strong>deploy</strong>, <strong>test</strong>, <strong>publish</strong></p>
  
  <p>The scenario:</p>
  
  <ul>
  <li>Run build</li>
  <li>Build finishes, but stages like <strong>publish</strong> are not executed</li>
  <li>Someone goes to some completed build and triggers the <strong>deploy</strong> or <strong>publish</strong> stage</li>
  <li>This triggers continuation of the pipeline. on the same build</li>
  </ul>
  
  <p>This will be much more convenient and user-friendly then running some other job with a Run Parameter. And it will keep the branch integrity.</p>
  
  <p>Is there a way to do such magic with Jenkins pipeline multibranch? </p>