title: Create new product relation / custom product relation magento 2
body: <p>I am trying to create a new tab in the admin area for product details where I can use a custom product relation. I am already using Upsell, Related and Cross-sell but would need an extra relation between products.</p>
  
  <p>Just wondering if anyone else has come against this issue/requirement and can point me in the right direction on creating a new product relation.</p>
  
  <p>Thanks!</p>