✨ Koenig - Support `/image {image url}` slash menu shortcut

refs https://github.com/TryGhost/Ghost/issues/9724
- add `src` param to the `image` card for use in the slash menu
- typing `/image http://example.com/image.jpeg` then pressing <kbd>Enter</kbd> will create an image card with the src pre-set

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

@@ -20,7 +20,8 @@ export const CARD_MENU = [
             icon: 'koenig/image',
             matches: ['image', 'img'],
             type: 'card',
-            replaceArg: 'image'
+            replaceArg: 'image',
+            params: ['src']
         },
         {
             label: 'Markdown',