Adapt app-driven entity page

Addresses the changes required after merging #2076. The Sentry plugin
now defines a router and the widget will be displayed as a tab.

plugins/sentry/package.json

@@ -21,6 +21,7 @@
     "clean": "backstage-cli clean"
   },
   "dependencies": {
+    "@backstage/catalog-model": "^0.1.1-alpha.21",
     "@backstage/core": "^0.1.1-alpha.21",
     "@backstage/theme": "^0.1.1-alpha.21",
     "@material-ui/core": "^4.9.1",
@@ -29,6 +30,7 @@
     "@types/react": "^16.9",
     "react": "^16.13.1",
     "react-dom": "^16.13.1",
+    "react-router": "6.0.0-beta.0",
     "react-sparklines": "^1.7.0",
     "react-use": "^15.3.3",
     "timeago.js": "^4.0.2"