title: Laravel Validation, a field should be 1 if another field is 0 and viceversa
body: <p>suppose, i have a request object which sends</p>
  
  <pre><code>[
   a =&gt; 0,
   b =&gt; 0
  ]
  </code></pre>
  
  <p>I want to have a validation, which will result to an error as both a and b are 0. I need at least one to be 1. how can I do that?
  Another working eg:</p>
  
  <pre><code>[
   a =&gt; 0,
   b =&gt; 1
  ]
  </code></pre>
  
  <p>it should pass</p>