title: Disable a step in CDK Stepper / prevent to go back to previous step
body: <p>I have a CdkStepper in my Angular app - consisting of 4 steps - which behaves quite regularly. No step is optional, so you cannot jump over any step, but the user can always go back to the previous step.</p>
  
  <p>CdkStepper: <a href="https://material.angular.io/cdk/stepper/" rel="nofollow noreferrer">https://material.angular.io/cdk/stepper/</a></p>
  
  <p>Now I have a <strong>special case</strong>, where the stepper is being opened directly at step 2, and in this case I need to <strong>disable the option to go back to the previous</strong> (the first ) step while still allowing to step back from 4 to 3 and 3 to 2.</p>
  
  <p>My code is similar to the example here:
  <a href="https://stackblitz.com/edit/angular-cdk-stepper-demo" rel="nofollow noreferrer">https://stackblitz.com/edit/angular-cdk-stepper-demo</a></p>
  
  <pre><code>&lt;vwlmz-stepper #stepper linear&gt;
      &lt;!-- Step 1 --&gt;
      &lt;cdk-step #step1="cdkStep"&gt;
          &lt;ng-template cdkStepLabel&gt;
              ...
          &lt;/ng-template&gt;
      &lt;/cdk-step&gt;
      &lt;!-- Step 2 --&gt;
      &lt;cdk-step #step2="cdkStep"&gt;
          &lt;ng-template cdkStepLabel&gt;
              ...
          &lt;/ng-template&gt;
      &lt;/cdk-step&gt;
      &lt;!-- Step 3 --&gt;
      &lt;cdk-step #step3="cdkStep"&gt;
          &lt;ng-template cdkStepLabel&gt;
              ...
          &lt;/ng-template&gt;
      &lt;/cdk-step&gt;
      &lt;!-- Step 4 --&gt;
      &lt;cdk-step #step4="cdkStep"&gt;
          &lt;ng-template cdkStepLabel&gt;
              ...
          &lt;/ng-template&gt;
      &lt;/cdk-step&gt;
  &lt;/vwlmz-stepper&gt;
  </code></pre>
  
  <p>StackOverflow and Google search didn't give me an answer.</p>