title: Checkout git repo with git submodules in Jenkinsfile with credentials
body: <p>I have a stage in my Jenkinsfile that look like:</p>
  
  <pre><code>stage('Pull Source Code') {
      steps {
          script {
              git branch: "master",
                      credentialsId: 'myCredentialId',
                      url: "${GIT_URL}"
          }
          sh 'git submodule update --recursive'
      }
  }
  </code></pre>
  
  <p>I want to provide credentials for the git git submodule update step because it giving the following error:</p>
  
  <pre><code>+ git submodule update --recursive
  Cloning into 'submodule-destination-folder'...
  fatal: could not read Username for 'https://tfsgit.mycompany.com': No such device or address
  fatal: clone of 'https://tfsgit.mycompany.com/submodule-repo' into submodule path 'submodule-destination-folder' failed
  </code></pre>
  
  <p>Is there a way to provide Jenkins credentials to git submodule update ?</p>