title: Jenkins pipeline: use parent job's params and add to them to call child job
body: <p>I have x2 declarative pipeline Jobs, both with many many params.
  How can I take the params provided to the parent, and add to them, to pass to the child job?</p>
  
  <p>I currently define them all individually, but this is prone to mistakes as there's a lot of them. </p>
  
  <p>I also have figured out it's possible to obtain a list of params and pass them to the child job:</p>
  
  <pre><code>script{
      def myparams = currentBuild.rawBuild.getAction(ParametersAction).getParameters()
      build( job: 'childJobName', parameters: myparams)
  }
  </code></pre>
  
  <p>What I haven't figured out is how to add to this list as it's unmodifiable. I'd need to make a copy and add to that, but I've not had any success doing this.</p>