feat: the app plugin

Co-authored-by: Patrik Oldsberg <poldsberg@gmail.com>
Co-authored-by: Fredrik Adelöw <freben@users.noreply.github.com>
Co-authored-by: Johan Haals <johan@haals.se>
Co-authored-by: Camila Belo <camilaibs@users.noreply.github.com>
Co-authored-by: Camila Belo <camilaibs@gmail.com>
Signed-off-by: blam <ben@blam.sh>

plugins/app-backend/package.json

@@ -6,6 +6,7 @@
     "role": "backend-plugin",
     "pluginId": "app",
     "pluginPackages": [
+      "@backstage/plugin-app",
       "@backstage/plugin-app-backend",
       "@backstage/plugin-app-node"
     ]