Add e2e test for browser integration on Bitbucket

Created by: felixfbecker

Ref #5294 (closed)

Tests only the browser extension, not the native integration, but lays the foundation for other browser extension tests. The browser extension has to be build with <all_urls> permissions because puppeteer cannot accept permission prompts.

This script would be run manually before release for now, but could run against our dogfood instance.