title: knockout set custom attributes with options binding
body: <p>I have a simple select multiple with options binding like below : </p>
  
  <pre><code>&lt;select multiple="multiple" width="50" data-bind="options: propositions, optionsText: function(item){ return item.name }, optionsValue: function(item) { return item.name }"&gt;&lt;/select&gt;
  </code></pre>
  
  <p>this is able to set item.name on the value attribute of the option item like below : </p>
  
  <pre><code>&lt;option value=" item.name value here ... "&gt; item.name also here &lt;/option&gt;
  </code></pre>
  
  <p>What I would like is to set a custom attribute like this : </p>
  
  <pre><code>&lt;option value=" item.name " data-value = " item.name "&gt; item.name also here &lt;/option&gt;
  </code></pre>
  
  <p>Is it possible to tell knockout to set the attribute <strong>data-value</strong> in the binding and how would you do that ?</p>