Added gifs card to card menu

refs https://github.com/TryGhost/Team/issues/1217

- behind the `gifsCard` feature flag
- currently maps to the unsplash image selector whilst we're building out an alternative selector

ghost/admin/lib/koenig-editor/addon/options/cards.js

@@ -211,6 +211,20 @@ export const CARD_MENU = [
                 imageSelector: 'unsplash'
             }
         },
+        {
+            label: 'GIF',
+            icon: 'koenig/kg-card-type-unsplash',
+            desc: '/gif [search-term or url]',
+            iconClass: 'kg-card-type-unsplash',
+            matches: ['gif', 'giphy', 'tenor'],
+            type: 'card',
+            replaceArg: 'image',
+            params: ['searchTerm'],
+            payload: {
+                imageSelector: 'unsplash'
+            },
+            feature: 'gifsCard'
+        },
         {
             label: 'Vimeo',
             icon: 'koenig/kg-card-type-vimeo',