feat(Avatar): handle icon default from app.config.ts

Author: benjamincanac

docs/content/2.elements/3.avatar.md

@@ -55,7 +55,7 @@ If there is an error loading the `src` of the avatar or `src` is null / false a
 
 #### Icon :u-badge{label="Edge" class="ml-2 align-text-bottom !rounded-full" variant="subtle"}
 
-You can use the `icon` prop to display an icon on top of the background, customizable in `ui.avatar.icon`.
+You can use the `icon` prop to display an icon on top of the background or globally in `ui.avatar.default.icon`.  Defaults to `null`.
 
 ::component-card
 ---

src/runtime/app.config.ts

@@ -113,6 +113,7 @@ const avatar = {
   },
   default: {
     size: 'sm',
+    icon: null,
     chipColor: null,
     chipPosition: 'top-right'
   }

src/runtime/components/elements/Avatar.vue

@@ -52,7 +52,7 @@ export default defineComponent({
     },
     icon: {
       type: String,
-      default: null
+      default: () => appConfig.ui.avatar.default.icon
     },
     size: {
       type: String,