feat: introduce collection of feature flags and make FlatRoutes treat feature flags as first class citizens

Co-authored-by: Johan Haals <johan.haals@gmail.com>
Co-authored-by: Patrik Oldsberg <poldsberg@gmail.com>
Co-authored-by: Fredrik Adelöw <freben@users.noreply.github.com>

Signed-off-by: blam <ben@blam.sh>

packages/app/package.json

@@ -8,6 +8,8 @@
     "@backstage/cli": "^0.7.0",
     "@backstage/core": "^0.7.12",
     "@backstage/integration-react": "^0.1.3",
+    "@backstage/core-app-api": "^0.1.1",
+    "@backstage/core-components": "^0.1.1",
     "@backstage/plugin-api-docs": "^0.4.15",
     "@backstage/plugin-badges": "^0.2.2",
     "@backstage/plugin-catalog": "^0.6.2",