Update sentry-javascript monorepo to v6 (#41991)

* Update sentry-javascript monorepo to v6

* Pass fetch implementation to FetchTransport and stub in unit tests

* kick drone

Co-authored-by: Renovate Bot <bot@renovateapp.com>
Co-authored-by: Ashley Harrison <ashley.harrison@grafana.com>

packages/grafana-runtime/package.json

@@ -26,7 +26,7 @@
     "@grafana/data": "8.4.0-pre",
     "@grafana/e2e-selectors": "8.4.0-pre",
     "@grafana/ui": "8.4.0-pre",
-    "@sentry/browser": "5.25.0",
+    "@sentry/browser": "6.15.0",
     "history": "4.10.1",
     "lodash": "4.17.21",
     "react": "17.0.1",