title: woocommerce: add value to a product attribute
body: <p>How do I add value to a woocommerce attribute through code?
  I have created an attribute called 'Dispatch time' (taxonomy: pa_dispatch) and now I want to add value to a particular product's Dispatch attribute.</p>
  
  <p>How to do this programmatically?</p>
  
  <p><img src="https://i.stack.imgur.com/WB1Hr.png" alt="enter image description here"></p>