title: Need to pass git sha to checkout to Jenkins multi branch pipeline
body: <p>Is it possible to use parameters to allow users to pass a git sha to a multi branch pipeline while defaulting to the head of the branch? Also I would only need to this function for the master branch.</p>
  
  <p>I'm using ...<br>
  Jenkinsfile in code<br>
  Jenkins Declarative Pipeline  </p>