Added redemption count for offers in list screen

closes https://github.com/TryGhost/Team/issues/1136

ghost/admin/app/models/offer.js

@@ -10,6 +10,7 @@ export default Model.extend(ValidationEngine, {
     status: attr('string', {defaultValue: 'active'}),
     tier: attr(),
     stripeCouponId: attr('string'),
+    redemptionCount: attr('number'),
     currency: attr('string'),
     type: attr('string', {defaultValue: 'percent'}),
     amount: attr('number'),

ghost/admin/app/templates/offers.hbs

@@ -63,7 +63,7 @@
                             </span>
                         </LinkTo>
                         <LinkTo @route="offer" @model={{offer}} class="gh-list-data">
-                            <span class="midgrey">-</span>
+                            <span class="midgrey">{{offer.redemptionCount}}</span>
                         </LinkTo>
                         <div class="gh-list-data gh-list-cellwidth-10 gh-tag-list-chevron">
                             <div class="flex items-center justify-end w-100 h-100">