feat(ui-devkit): Add `prefix` option to route config to allow overrides

Relates to #2705. This option allows you to define custom routes which will override
the built-in routes in the Admin UI.

packages/ui-devkit/scaffold/src/app.routes.ts

@@ -14,6 +14,10 @@ export const routes: Route[] = [
             breadcrumb: _('breadcrumb.dashboard'),
         },
         children: [
+            // Defining the extension routes before the built-in routes allows
+            // the extension routes to take precedence over the built-in routes, enabling
+            // the extensions to override built-in functionality.
+            ...extensionRoutes,
             {
                 path: '',
                 pathMatch: 'full',
@@ -43,7 +47,6 @@ export const routes: Route[] = [
                 path: 'system',
                 loadChildren: () => import('@vendure/admin-ui/system').then(m => m.SystemModule),
             },
-            ...extensionRoutes,
         ],
     },
 ];

packages/ui-devkit/src/compiler/scaffold.ts

@@ -183,8 +183,9 @@ function generateLazyExtensionRoutes(extensions: AdminUiExtensionWithId[]): stri
             }
         }
         for (const route of extension.routes ?? []) {
+            const prefix = route.prefix === '' ? '' : `${route.prefix ?? 'extensions'}/`;
             routes.push(`  {
-    path: 'extensions/${route.route}',
+    path: '${prefix}${route.route}',
     loadChildren: () => import('./extensions/${extension.id}/${path.basename(route.filePath, '.ts')}'),
   }`);
         }

packages/ui-devkit/src/compiler/types.ts

@@ -136,8 +136,28 @@ export interface AdminUiExtension
      * relative to the `extensionPath` which exports an array of Angular route definitions.
      */
     routes?: Array<{
+        /**
+         * @description
+         * The name of the route. This will be used as the path in the URL.
+         */
         route: string;
+        /**
+         * @description
+         * The path to the file which exports an array of Angular route definitions.
+         */
         filePath: string;
+        /**
+         * @description
+         * All extensions will be mounted under the `/extensions/` route. This option allows you to specify a
+         * custom prefix rather than `/extensions/`. For example, setting this to `custom` would cause the extension
+         * to be mounted at `/custom/<route>` instead.
+         *
+         * A common use case for this is to mount the extension at the root of the Admin UI, by setting this to an empty string.
+         * This is useful when the extension is intended to replace the default Admin UI, rather than extend it.
+         *
+         * @since 2.2.0
+         */
+        prefix?: string;
     }>;
 
     /**