Collect coverage for end-to-end playwright tests

[daanboer]

Currently we don't produce coverage reports for the end-to-end tests in CI. It would be nice to collect coverage and add the reports to Codecov to get a complete overview of all tests that are run. However, it seems relatively hard to set this up in conjunction with Nextjs (SSR in particular). Nonetheless, there are some resources available, see e.g.:

• The playwright docs
• bgotink/playwright-coverage
• mxschmitt/playwright-test-coverage